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Now the engine mini-tiller has become indispensable agricultural machinery in vast hilly and mountainous areas of Southwest China. Many researches have been made to improve its operating comfort, but little effects have been obtained. As an alternative, a new type of electric mini-tiller was developed. For further improvement of its operating comfort, simulation analysis and field test were integrated to decrease the vertical force and vibration RMS values at the handle. The results showed that when the position of centre of gravity moved 19.78 cm, the vertical force was reduced from 154.24 N to 0 N, and vibration RMS values decreased by 20.16% under working condition. 摘要 目前,微耕机已经成为中国西南广大丘陵山区不可缺少的农业机械。为了改善其操作舒适性,做了许多研究, 但是效果很小。因此,开发了一种新型电动微耕机,为了进一步改善其操作舒适性,采用仿真分析和田间试验 相结合的方法来减小扶手处的垂向力和振动加速度值。结果表明,在正常工作条件下,当重心位置移动 19.78 cm时,垂向力由 154.24 N减小到 0 N,振动加速度值减小 20.16%。 INTRODUCTION Being small volume, light weight, simple structure and easy transfer in the farm land, the internal combustion engine mini-tiller has become the main and indispensable agricultural machinery in the hilly and mountainous area of Southwest China (Chen J. et al, 2014). However, there have been urgent needs of improvement of its operating comfort, especially nowadays, for most tiller operators are women and aging people in the area. The mini-tiller is a kind of walking machinery and its operating comfort mainly relies on the vibration acceleration and the force applied to the operator’s two hands through the tiller’s handles. Therefore, decreasing the both can make the operating comfort increase. The tiller’s engine vibration is mainly caused by two coupling effects of cycling movement of the pistonconnecting rod of the engine and periodical rotary blades cutting soils. The vibration acceleration at the handle can be reduced from two aspects: reducing vibration or obstructing vibration transmission from its resources to the operator's hands (Ying Y.B. et al, 1994; Ragni L, 1999; Dong X.Q. et al, 2012; Xu L.Z. et al, 2014). Bini and Kathirvel deals with machine vibration, hand transmitted vibration of walking and riding type power tillers during rototilling in untilled and tilled fields and in transport mode on farm and bitumen roads. The results indicate that machine vibration increased with the increase in engine speed and major excitation of the power tiller vibration was the unbalanced inertial force of the engine (Bini and Kathirvel, 2006). Tewari and Dewangan pointed that the operators of hand tractors experience high levels of vibration in the hand and arm, which cause early fatigue and result in shorter working hours. Suitable isolators were designed and installed in different strategic locations in the hand tractor in order to reduce the effect of vibration level, and hence reduce work stress. The results indicated that the engine mounting and the handle isolators reduced the vibration acceleration by more than 50% (Tewari and Dewangan, 2009). Liang Xincheng et al. selected 1Z-105 diesel mini tiller as a prototype, its vibration characteristics were analysed in the time and frequency domains and the effects on the human body were explored, and suggestion was made regarding the handling comfort of the mini tiller (Liang X.C. et al, 2018). But these researches have little effect; the main reasons lie in implementation of measures stated above being difficult without a substantial increase in size, weight and price of the tiller (Thomas H.L. et al, 2015; Caffaro F. et al, 2016; Niu P. et al, 2017), which is unacceptable for local the farmers. Vol. 60, No. 1 / 2020 INMATEH – 222 As a countermeasure, a new type of electric mini-tiller was developed, which can achieve a tillage depth of 10 cm or more and replace the engine tiller for farming operations in dry land tillage and land preparation in vast hilly and mountainous areas of Southwest China. Because its power is a group of lithium battery and a brushless DC motor instead of combustion engine, its vibration resulting from the power is decreased, but the vibration caused by periodical rotary blades cutting soils still exists, further efforts are needed. Until now, vibration of electric mini-tillers has not captured much researchers’ attentions, perhaps because unlike the one mentioned above, the majority of existing ones were only suitable for shallow tillage, in other words, they can get a tillage depth of about 5 cm (Cai K. et al, 2013; Gao H.S. et al, 2012; Zhao R.H. et al, 2015). Therefore, vibration produced by these kinds of electric mini-tillers is not so intense. The other factor that influences tiller’s operating comfort is the force applied to operator’s hands. It can be decomposed into three components along three directions, namely, top-bottom, left-right and front-back. Under normal circumstances, the latter two components are small and uncontrollable compared with the first one (Hu C.J., 2018). So, the component of the force in the direction top-bottom, i.e. the vertical force should be carefully considered to increase the operating comfort. When cultivating clay soil, a certain vertical force is necessary to ensure adequate tillage depth. However, under some soil conditions, a small force is sufficient. Therefore, the determination of the best vertical force for different soils is a problem worth exploring, but so far there are few reports about it. In this study, the newly developed electric mini-tiller mentioned above was taken as the research object, the method of combining three-dimensional modelling, force analysis, simulation analysis and field test was adopted to decrease its vibration and vertical force at the handles and improve its operating comfort by changing the position of the tiller centre of gravity, so as to provide available theory and reference to improve the operating comfort of tillers. MATERIALS AND METHODS Electric mini-tiller The electric mini-tiller is mainly composed of handrail, motor controller, electric motor (brushless DC motor, rated power, 0.75 kW), battery pack (60V20Ah lithium battery), rotary blade roller (type of blade, machete; no. of blades, 4×3), transmission system (direct drive), frame, and depth-limiting device, as shown in fig.1. The transmission system consists of power input shaft, one pair of straight bevel gears and power output shaft. The significant parameters of the tiller are listed in table 1, and the material properties of its primary components are delineated in table 2. Fig. 1 Electric mini-tiller 1 –Handrail; 2 –Motor controller; 3 –Electric motor; 4 –Battery pack; 5 –Rotary blade roller; 6 –Transmission system; 7 –Frame; 8 –Depth limiting device

IMPROVING THE OPERATING COMFORT OF THE ELECTRIC MINI-TILLER BASED ON SIMULATION ANALYSIS AND FIELD TEST