342 E. Velazquez-Miranda et al. Fig. 36.1 Schematic diagram of the mechanical system under evaluation vibration can lead to disorders in bones, joints, muscles, and even circular and neurological disorders. Therefore, standards and regulations have been developed for the measurement of vibrations in humans due to these effects, such as the ISO 2231-5on Mechanical Vibration and Shock-Evaluation of Human Exposure to Whole-Body Vibration, and the ISO 5349 on Mechanical Vibration-Measurement and Evaluation of Human Exposure to Hand Transmitted Vibration[3, 4]. The vibrations in agricultural equipment have been widely studied by various authors. However, the evaluation of smallscale machinery has been carried out mainly in countries where the agricultural sector is predominant. For example, the structural analysis of equipment for the preparation of germinative beds has been studied by [5] with the objective of analyzing the frequencies at which resonances occur in working conditions. On the other hand, the evaluation of vibrations in a mini-tiller, with an analysis in different speed ranges, finding that the vibration comes from the unbalanced forces of the engine, was reported by [6]. Also, considering different modes of operation, [7] describes the characteristics of hand-transmitted vibration of a hand tractor making an analysis of variance to identify the effects of different directions of vibration acting on the human being. The structural optimization of a tiller handheld was made by [8] through the results of a computational and experimental modal analysis, whose results were evaluated by the analysis of variance to determine the appropriate dimensions of the handrail to reduce vibrations. With this same purpose, [9] proposed the use of damping materials to reduce hand transmission vibrations to the operator such as polyurethane and synthetic rubber, finding that the latter was the best option during the transportation, tilling and rota-tilling modes of the machine. Previous studies characterize and study the transmission of vibrations in agricultural machines. Considering a systemic approach, the handlebar of the two-wheel tractor is the medium that transmits to the human being the vibrations of the machine (endogenous excitation) and the soil-machine interaction (exogenous excitation). The importance of humanmachine interaction is that the human being is an articulated mechanism composed of rigid bars (bones) joined by joints so a human can be considered as an open kinematic chain that is exposed to excitement through the handlebar. For this reason, it is essential to know the frequency ranges that influence the discomfort and physical damage of the human being. The frequency ranges present in human hand-arm has been studied by [10] through finite element analysis and operational modal analysis with the aim of understanding the mechanisms of injury in the hand-arm system. In this work the transmissibility of the vibrations was in a range of 2.6–244 Hz, finding that the frequencies related to effects on the wrist, elbow, and shoulder are in the order of 12.36 and 97 Hz. In this context, the analysis of the vibrations present in the human being due to the excitation of agricultural machinery such as the two-wheel tractor is an aspect that must be addressed, since agricultural work requires exposure of the farmer to the effects of vibrations for extended periods of time. Likewise, the minimization of the acceleration components at the point of contact with the farmer reflects the importance of the redesign of the handlebar through the design of passive or semi-active systems adaptable to existing machinery since being a simple machine at a technological level and used by small farmers, it is necessary to consider the economy-functionality relation of the machine. For this purpose, and in the framework of a systemic approach, Fig. 36.1 shows the evaluation system and the variables involved in the study of human-structure-soil interaction on the Two-Wheel tractor. 36.3 Modal Analysis of a Two-Wheel Tractor Handlebar The mechanical system used in the analysis consists of a 6.5 hp commercial two-wheel tractor used in greenhouse agriculture. The modal analysis of the two-wheel tractor is focused on the analysis of the handlebar, since it is the point where there is a direct interaction with the human (farmer). Figure 36.2 shows the main components of the machine used in the analysis. The modal analysis to estimate the natural frequencies of the two-wheel tractor was carried out by means of a computational modal analysis and the experimental modal analysis. The 6.25 kg handlebar structure was modeled using the finite element method (FE) considering that the handlebar material is a structural steel AISI 1020 with Young Modulus
RkJQdWJsaXNoZXIy MTMzNzEzMQ==