بررسي ارگونوميكي ارتعاش يك نوع روتوتيلر با تيغه‌هاي جديد

Ergonomic Evaluation of Vibrations of a Rototiller with New Blade

یكی از مهم‌ترین بحث‌ها در مكانیزاسیون كشاورزی مسئله سلامتی انسان هنگام كار با ماشین است كه امروزه به یك موضوع برجسته در علم ارگونومی تبدیل شده است. ارتعاش منتقل شده از دسته‌ی روتوتیلر به دست، بازو و بدن راننده ممكن است در طولانی مدت منجر به بروز صدمات زیادی ازجمله ناراحتی‌های عصبی، درد و اختلالات اسكلتی و عضلانی شود. از این رو در پژوهش حاضر پارامترهای ارتعاشی یك نوع روتوتیلر جدید مجهز به تیغه‌های لبه مضرسی به‌صورت آزمایش فاكتوریل در قالب طرح بلوك‌های كامل تصادفی در سه تكرار مورد بررسی قرار گرفت. اندازه‌گیری در سه سطح سرعت دورانی تیغه‌ها (170-140، 200-170 و230- 200 دور بر دقیقه) و دو وضعیت كاری (درجا و در حال خاك‌ورزی) انجام شد. نتایج نشان داد كه اثر وضعیت كاری و سرعت دورانی تیغه‌ها بر جذر میانگین مربعات شتاب كل (RMS) و مؤلفه‌های شتاب در جهت‌های x، y و z معنی‌دار بود. با افزایش سرعت دورانی تیغه‌ها از سرعت كم (rpm 155) به سرعت زیاد (rpm 215)، RMS شتاب كل به مقدار ms-2 9/12 افزایش یافت. حداقل سهم موتور مورد استفاده در ایجاد ارتعاش دستگاه در دور rpm 155 محور دوار، %53/65 و حداكثر آن در دور rpm 215 برابر با %92/73 به‌دست آمد. بالا بودن سهم موتور در ارتعاش نشان‌دهنده اهمیت انتخاب دور مناسب و موتور احتراقی با كیفیت بالاتر جهت كاهش ارتعاش كل دستگاه می‌باشد. بیش‌ترین زمان مجاز مواجهه با ارتعاش در حالت خاك‌ورزی مداوم كه كم‌تر از 2 ساعت است، در سرعت دورانی rpm170-140 به‌‌دست آمد.

<strong >Introduction </strong > One of the most important problems arising with operation of the conventional rototillers is severe vibration of the machine handle which is transmitted to the user’s hands, arms and shoulders. Long period exposure of the hand-transmitted vibration may cause various diseases such as white finger syndrome. Therefore in this study, vibrations of a new type of rototiller with ridged blades were investigated at the position of handle/hand interface in different working conditions. Finally, the maximum allowable exposure time to the rototiller users in continuous tillage operation was obtained according to ISO 5349-1. <strong >Materials and Methods </strong > Experiments were carried out in one of the farms with silty clay soil texture, located in Sari city, Mazandaran province, Iran. Vibration measurements were performed according to ISO 5349-1 and ISO 5349-2 standards in two different modes, including in situ mode and tillage mode. Vibrational parameters were obtained in three blade rotational speeds, i.e., low speed (140-170 rpm), medium speed (170-200), and high speed (200-230). Blade rotational speed varied by changing engine speed using the throttle control lever. In each experiment, different vibrational values were individually recorded in three directions (x, y, and z). Experimental design and data analysis were performed in a Randomized Complete Block Design with three replications using the SPSS16 software. <strong >Results and Discussion </strong > Based on the obtained results in this study, the RMS of acceleration increased by increasing in rotational speed for all of the conducted experiments. The reason is that number of cutting per unit of time and consequently the frequency of changing in the dynamic forces exerting on the blades dramatically increases with increasing the rotational speed of the blades. Noteworthy is that in most cases the variation of acceleration in the tillage mode showed similar trend with vibrational values in the idling mode. This represents a significant contribution of the combustion engine in vibration of the examined rototiller. Meanwhile, contribution of the engine in the total measured vibration was more than 50% at different rotational speeds and different directions. The minimum engine contribution was measured equal to 56.39% in z-direction at 155 rpm, whereas the maximum engine contribution was observed equal to 79.5%, in x-direction and rotational speed of 215 rpm. These results indicate the importance of selecting a proper combustion engine for reducing the rototiller vibration. It should be noted that the contribution of the engine in total vibration reached its minimum value at the speed related to the maximum generated torque, i.e., 185 rpm of the rotor speed. This result indicates that using the combustion engine in its optimum speed reduces the entire device vibration in the vertical direction. By increasing the rotational speed of the blades in the y-direction, engine contribution in device vibration showed different trends in compare to the other directions. The most value was equal to 74.25% which was obtained at the rotation speed of 185 rpm. By increasing blade rotational speed from 155 rpm to 215 rpm, the engine contribution in device vibration in the z direction and the total acceleration steadily increased. <strong >Conclusions </strong > With growing mechanization and entering various types of machines to the farm, importance of considerations to human health is also increased, especially in working with rotational machines. Therefore, the current study was undertaken with the specific attention to the rototillers operational vibration at the handle/hand interface. Results of the conducted experiments showed that vibration of the examined rototiller depends more on the operation of the mounted combustion engine, rather than the soil working blades. Therefore, it is suggested to select a higher quality engine with less vibration or isolate the engine from chassis by a damper (such as a compressed rubber) to reduce the vibration transmitted to the operator’s hands and arms.