Dynamic Behavior Analysis of Grass Trimmer Using Finite Element Method

Abstract

Dynamic behavior analysis of structural components is one of the important tasks in the design process of any mechanical system. Nowadays research personnel are intended to carry out research in this area to increase the efficiency and functionality of mechanical systems. The vibrational characteristic is very important in many dynamic machine components design and analysis. Among these machine structures, grass trimmer is one of the most common machines that exposed to the dynamic and static forces, coming from the engine and rotating blade. Prolonged exposure of grass trimmer leads to hand-arm vibration (HAV) syndrome to the operator. In this research, the dynamic behavior analysis of grass trimmer is performed by taking the dimension of the existing grass trimmer available with workers at NIT Rourkela. In totality, nine numbers of models are developed by changing the handle positions from cutter head as 1000, 1100, and 1200 mm at an angle of 90°, 60°, and 45°, alternatively. Harmonic analysis is carried out to evaluate the sustainable, dynamic behavior of the grass trimmer by estimating the natural frequencies and mode shapes. Based on the harmonic analysis, it is observed that model with 1100 mm @ 60^° handle position from cutter head is the optimum position because at this point vibration induced is least as compared with other models. After finding optimum handle position, a new handle design is proposed with a rubber mount and a thin cover of thickness 2.5 mm attached in between the shaft and handle. The analysis is performed on new design and found that the root mean square (RMS) value of the average acceleration at handle position is reduced appreciably as compared with the existing grass trimmer.