歩行式トラクタの振動特性の把握と伝達経路解析に基づく目標振動参照点の検出

概要

九州大学学術情報リポジトリ
Kyushu University Institutional Repository

Investigation of Vibration Characteristics of a
Hand Tractor and Detection of Target Vibration
Reference Points based on Transfer Path
Analysis Technique
プン, ソバタナ

https://hdl.handle.net/2324/6787680
出版情報：Kyushu University, 2022, 博士（農学）, 課程博士
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Name: プン ソバタナ（Phon Sovatna）
Title: Investigation of Vibration Characteristics of a Hand Tractor and Detection of Target
Vibration Reference Points based on Transfer Path Analysis Technique
（歩行式トラクタの振動特性の把握と伝達経路解析に基づく目標振動参照点の
検出）
Category: Kou

Thesis Summary
In Cambodia, agricultural mechanization has recently improved agricultural labor savings, energy
efficiency, productivity, and profitability, instead of conventional farming using livestock and human power.
In Southeast Asian countries, including Cambodia, walking tractors are the most widespread agricultural
machinery, especially in rural areas, where they have also been used for multiple purposes transportation and
mobility. Therefore, the operator is exposed to mechanical vibration for a long time, resulting in fatigue and
discomfort due to agricultural work in the field and driving on farm roads and public roads. With the above
background, to reduce the vibration of the walking tractor, the objectives of this study are 1) to grasp the
vibration characteristics of the walking tractor, 2) to obtain essential characteristics of transmission between
vibration on the handgrip, where the vibration is transmitted directly to the operator, and other parts of the
walking tractor, and 3) to identify reference parts with high vibration contribution to the handgrip.
Chapter 1 outlines the current state of agricultural mechanization in Cambodia, the popularity and use
of walking tractors, and the effects of vibration exposure on operators. In addition, the objectives of this
study were clarified by reviewing issues related to previous measurement methods for the vibration
characteristics of walking tractors and the evaluation of vibration exposure to operators. Furthermore, the
importance of reducing the vibration of walking tractors and detecting reference parts with high vibration
contribution to the handgrip is clarified.
In Chapter 2, a walking tractor's vibration intensity and frequency characteristics were investigated
under long operation conditions on Cambodia's farm roads. MEMS inertial sensors were installed at four
locations (handgrip, engine cover, chassis frame, and top of gearbox) to measure translational acceleration
and rotational angular velocity. The results showed that the vertical acceleration at the handgrip was the
largest, followed by the engine top, gearbox, and chassis in the idling condition. In the actual traveling case
(average speed: 1.4 m/s), the handgrips, followed by the engine top, generated the most considerable
vibration, indicating that the handgrips, which directly exposed the operator to the vibration, had greater
vibration intensity than the parts closer to the vibration source. Furthermore, a frequency analysis of the
measurement time series was also conducted. As a result, although the primary frequency component peaked
at a period corresponding to the engine speed at all measurement points, multiple peaks appeared at low
frequencies during traveling. These results indicate that it is necessary to investigate hand tractors' vibration
characteristics at different engine speeds and driving speeds.
In Chapter 3, to clarify the essential vibration characteristics of a walking tractor, inertial sensors were

installed at a total of seven locations: at the handgrip, where vibration is directly transmitted to the operator,
and at the top of the engine, front, rear, chassis frame, top of the gearbox, and center of the hand-arm, as
determined by the rigidity of the machine and the source of vibration. Simultaneous 3-axis translational
accelerations were measured at each of the above seven locations following the ISO standard (ANSI/ASA
S2.70-2006) for measuring vibration exposure of handgrip sections under idling conditions. The Power
Spectral Density (PSD) and the root mean square (RMS) were calculated from time series data of the
accelerometer of each part, and the frequency characteristics and vibration intensity at seven measurement
points on the walking tractor were compared. Furthermore, the vibration of the walking tractor was
evaluated based on the WHO health risk index for vibration exposure. As a result, it was shown that the
RMS values of acceleration of the hand-arm part exceeded healthy limits at all engine speeds.
In Chapter 4, to reduce the tractor's body vibration, especially the vibration of the handgrip, the inertia
sensors were installed at the seven locations shown in Chapter 2. They were used to measure the vibration
during dynamic driving. In addition, Transfer Path Analysis (TPA) was performed to clarify the transfer
locations contributing to the vibration of the handgrip. In the TPA, the vibration of the handgrip was taken as
the response (target) point, and the vibrations of the other six locations as the reference points. The
third-order tensor data of the PSD of the measured response and the reference points’ accelerations at
different running speeds were decomposed of singular values. The Root Mean Square Error (RMSE)
between the measured and the estimation reconstructed of the response point data with the contributing
components was calculated to detect the highest contributing reference point. As a result, it was found that
the chassis and the upper part of the gearbox were the most effective locations for vibration transmission to
the handgrip.
The primary results and implications of this study are summarized in Chapter 5. The measured
acceleration time series at seven locations on the hand tractor showed that the lateral vibration at the top of
the engine was the largest at low frequencies. The vertical vibration of the handgrip section has large values
over all frequencies. In addition, the vibration of the hand-arm and handgrip exceeded the WHO guideline at
all engine speeds. Therefore, vibration measures are necessary. Furthermore, the vibration of the handgrip of
a walking tractor is highly dependent on the vibration of the chassis and gearbox based on the analysis of
transmission paths, and it was suggested that anti-vibration measures be applied to these locations to reduce
vibration on the handgrip.

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