Introduction
Hand/arm vibration (HAV) is a major physical hazard in agricultural operations, particularly for operators of hand-held and walk‑behind machinery. Prolonged exposure can lead to Hand/Arm Vibration Syndrome (HAVS), vibration-induced white finger (VWF), and musculoskeletal disorders, reducing work efficiency and operator well‑being. Paddy weeders, operating in soft and uneven wetland soils, are subject to severe dynamic loads that intensify vibration transmission to the operator's hands. Although previous studies have investigated vibration in agricultural machinery and proposed various reduction strategies, limited information exists regarding the directional effectiveness of rubber isolators, particularly Styrene‑Butadiene Rubber (SBR) under varying engine speeds. The physical mechanisms governing vibration energy dissipation, especially the role of geometric asymmetry along different orthogonal axes, remain poorly understood. Therefore, this study aimed to: (1) quantify the effectiveness of an SBR rubber isolator in reducing handle vibration of a paddy weeder at three engine speeds (3200, 4800, and 6400 rpm); (2) investigate the simultaneous effects of engine speed and isolator presence on vibration along the X, Y, and Z axes; (3) analyse the physical mechanisms of vibration reduction based on viscoelastic energy dissipation and frequency response theory; and (4) identify geometric factors governing the directional performance of the isolator.
Materials and Methods
A paddy weeder equipped with, a four‑stroke, spark ignition, air‑cooled engine (working width: 60 cm, rotor diameter: 40 cm, six flanges, three rows of weeding elements) manufactured by Elm-o-Fannavary Tabarestan Company, Iran, was used. An SBR rubber isolator (thickness: 5 mm, width: 50 mm, effective dynamic stiffness: 100 N mm^-1) was installed between the machine frame and the handle mount. The natural frequency of the handle‑isolator system was estimated at 35.6 Hz, yielding frequency ratios (r = f/fₙ) ranging from 1.5 to 3.0 across the tested speeds, placing all operating conditions within the vibration isolation region (r > √2). Vibration measurements were conducted according to ISO 5349‑1 (2001) using a VB‑8202 vibrometer (Lutron, Taiwan) with a frequency range of 10 Hz to 1 kHz and an acceleration range of 0.5–199.9 m s^-². The root mean square (RMS) acceleration components were recorded along three orthogonal axes (X, Y, and Z) under two conditions (with and without isolator) at three engine speed levels. The experiment was designed as a factorial experiment with three replications. Data were analysed using two‑way ANOVA at the 1% and 5% significance levels. Theoretical frequency response functions and viscoelastic energy dissipation models were derived to interpret the experimental observations.
Results and Discussion
The ANOVA results revealed that engine speed had a highly significant effect (p < 0.001) on handle vibration along all three axes, with vibration amplitude increasing proportionally to the square of rotational speed (R² > 0.95), confirming theoretical predictions from the frequency response model. The rubber isolator significantly reduced vibration along the X (p = 0.014) and Z (p < 0.001) axes, while its effect on the Y axis was not statistically significant (p = 0.099). No significant interaction effects were observed between engine speed and isolator conditions (p > 0.05).
The most substantial vibration reduction (90.63%) was observed in the Z direction at 6400 rpm, where RMS acceleration decreased from 192 m s^-² (without damper) to 18 m s^-² (with damper). At low speed (3200 rpm), the damper showed minimal or adverse effects, particularly along the Y axis where a 10.34% increase was recorded (from 29 to 32 m s^-²). At medium speed (4800 rpm), a moderate reduction of approximately 4–65% was observed across different axes, with the Z direction showing a 65.71% reduction (from 70 to 24 m s^-²).
Mechanical analysis based on viscoelastic energy dissipation models demonstrated that the superior performance along the Z axis was attributable to the isolator's geometric configuration. The effective deformation length in the Z direction (50 mm width) was approximately ten times greater than that in the X direction (5 mm thickness), leading to substantially higher cyclic strain and approximately 2.9 times greater energy dissipation per cycle. This theoretical prediction was validated experimentally, showing a 2.2‑fold higher reduction ratio in the Z direction compared with the X direction at high speeds. The frequency response function further explained the enhanced attenuation at higher speeds, where increasing frequency ratios reduce the transmissibility of the handle‑isolator system.
Conclusion
This study systematically quantified the directional effectiveness of an SBR rubber isolator in reducing hand‑transmitted vibration of a paddy weeder under varying engine speeds. The key findings are:
1. Handle vibration amplitude increased significantly with engine speed, following a quadratic relationship (R² > 0.95) consistent with theoretical predictions.
2. The rubber isolator exhibited strongly direction‑dependent performance. The highest vibration reduction (90.62%) was achieved in the Z direction at 6400 rpm, attributed to the larger deformation path and enhanced viscoelastic energy dissipation resulting from geometric asymmetry.
3. At low engine speeds (3200 rpm), the isolator was ineffective and even increased vibration along the Y axis (≈2%), confirming that effective isolation requires the frequency ratio to substantially exceed √2.
4. No significant interaction was found between engine speed and isolator condition, indicating independent and predictable contributions of each factor, which facilitates future design optimisation.
5. The close agreement between theoretical predictions (energy dissipation and frequency response models) and experimental measurements validates the proposed analytical framework and provides a robust basis for engineering design.
These findings demonstrate that carefully engineered rubber isolators, with geometry tailored to the dominant vibration direction and operating speed, represent a practical, cost‑effective strategy for mitigating harmful vibrations in light agricultural machinery. This approach improves operator health and comfort, enhances work efficiency, reduces fatigue, and contributes to sustainable agricultural practices. Future research should focus on geometric optimisation, finite element modelling, comparative evaluation of advanced elastomeric materials, and durability assessment under prolonged field conditions.