Dynamic Behaviour Analysis of Grass Trimmer Using Finite Element Method

Abstract

Dynamic behavior of structural components is one of the important parts in the design process for any mechanical system existing in the world now-a-days and lots of research is carried out in order to increase their efficiency and functionality. In order to determine the dynamic behavior of a vibrating structure, measurements of the dynamic properties of structure are essential. The importance of determining these vibration characteristics are crucial as grass trimmer is a common machine that exposed to the dynamic and static forces coming from the engine and rotating blade. A long term exposure of grass trimmer’s operator may or potentially suffering a risk of hand arm vibration syndrome. In this project, the modal analysis and harmonic response of grass trimmer was performed using commercial finite element software, such as Ansys. One CAD modal was made by taking the dimension of exiting grass trimmer. After that, by changing the three handle positions of the cutter head (1000mm, 1100mm, and 1200mm) and three different angle (45◦ , 60◦ and 90◦ ), nine model were developed to determine the dynamic behavior of grass trimmer like natural frequency and mode shape and at different natural frequency deformation calculated. Harmonic analysis was carried out to evaluate the handle vibration. It was found that 1100 mm handle position from cutter head, optimum position because at this point vibration induced was less in comparison of 1000 mm and 12000 mm handle position from cutter head. Again one new handle was designed with rubber mount and 2.5mm thin cover put on the shaft. Six model were developed by changing the handle material and cover on the shaft. Natural frequency and mode shape was determined. Harmonic analysis was also carried out to determine the handle acceleration. It was found that at handle point average acceleration in three axes was less at handle angle (60◦) and rms value of average acceleration of three axes was 47% less in comparison of existing grass trimmer.