チェーンソー振動の多自由度解析 (I) : 防振構造の比較

Abstract

チェーンソーの防振構造を解析し, より防振効果の優れたものを模索した。現在, 我国で使用されている機種の中より防振構造の異なる機種を選び振動加速度, 起振力, 防振構造の諸量を測定した。防振構造の特徴, 防振効果等を測定より得た前後ハンドル比, コンプライアンス, 周波数分析, さらに理論演算によるハンドルに伝達される力の推定値で考察した。1. ハンドル把持部での振動加速度値は防振構造内の共振に影響され, 前後ハンドルで異った傾向を示すが, その間には一定の規則性が見られた。2. 防振構造の特性を示すコンプライアンスより, 6自由度系の剛体モデルはある程度の意義が確認された。しかし, 実際のコンプライアンスは防振構造が弾性体として種々の固有振動数をもってふるまうため, 剛体として取り扱えない面が存在していた。3. 防振ハンドル各部の固有振動数が常用回転数域にあると, その周波数を機関回転数とする際に振動加速度値は共振によって増大する。4. 防振ハンドルの重量がより大きいタイプの防振構造は振動加速度値がより小さいという傾向を示すが, ハンドルに伝達される力はハンドルと機関本体との質量比が不釣合なたあ大きくなると考えられる。

In Japan, several steps have been taken to prevent the operator of chainsaw from 'white finger' induced by its vibration. Firstly, the limit of operating time of chainsaw has been set as two hours in a day. Secondly, the national parties have developed several equipments of chainsaw in order that man may operate chainsaw without holding it, for example, remote-controlled chainsaw. But, almost operators are yet driving AV-chainsaws as before. So they are exposued by excessive noise and vibration of chainsaw even now. Judging from these states, we must reduce vibration of chainsaw by improving on AV-chainsaw. Several types of AV-chainsaw are used in Japan. Then, to investigate each performance of chainsaw to isolate vibration, we measured the vibration at top and back handle, and the inertia force by engine about several chainsaws (Fig. 5, 6). On the other hand, we treated chainsaw as a rigid body system with the six degrees of freedom and analized its vibration. From them, we calculated the ratio of amplitudes of displacement at top to back handle (Fig. 2) and the ratio of amplitude of displacement at handle to the inertia force by engine (Fig. 7), so called as compliance, and compared these ratios from the meausrements with the ones from the model, and gave thought to the theoretical ratio of the transmitted force to handle and the external alternating force (Fig. 8). By this study, we reached the following conclusions. The method of this model nearly indicates the isolating performance of vibration about each AV-chainsaw. Therefore, we shall investigate AV-chainsaw in this model and decide both the division of mass and the location of isolators from vibration. But there are a few points of resonance in the AV-chainsaw within 40-150 Hz. So the amplitudes of acceleration at handle are amplified by these resonances when the revolutions of shaft per second are in accord with them. We cannot grasp this tendency in this model. This tendency may originate in the elastical feature of AV-chainsaw. Then we shall inquire further into the problem by the method of elastical model. (AV-chainsaw; anti-vibration chainsaw)