Optimization of operating parameters for a back-pack type grass trimmer

Hand–arm vibration syndrome (HAVS) is very common among workers operating power tools and performing similar work for extended period of time. Grass trimming involves the use of motorized cutter spinning at high speed, resulting in high levels of hand–arm vibration (HAV) among the machine operators. In this study the influence of handle–hand interaction of a grass trimming machine (GTM) is evaluated based on different hand positions of operator during operation. Besides, several operating parameters (length of nylon cutting thread, engine speed and sway angle) are investigated in terms of HAV. Three handle–hand positions (HHPs) are studied that are generally adopted by the GTM operators during their work. Data are analyzed via orthogonal array, main effect, signal-to-noise (S/N) ratio, and analysis of variance to determine the appropriate operating parameter levels and HHP to minimize HAV. HHPs and operating parameters under investigation are found to be influential in controlling HAV generation during grass trimming operation. Experiments are carried out for measuring hand vibration using a tri-axial accelerometer conforming the effectiveness of this approach. It is shown that among the three HHPs considered in this study, optimum result in terms of HAV is 2.42 m/s2. Moreover results show that 170 mm length of nylon thread, 3000±400 rpm of engine speed and 45° of sway angle combination results in minimum HAV (HARM) of magnitude 2.42 m/s2. Through this study not only the optimal operating parameter levels for GTM are obtained, but also the main process parameters that affect the HAV are determined. The optimum HAV obtained through appropriate selection of HHP and operating parameters, significantly reduces the occurrence of HAVS among the grass trimmers.Relevance to industryThe paper discusses the evaluation of HAV for GTM, which is widely used in Malaysia for grass trimming operation especially by the side of highways. A large number of workers are employed by the highways authority for this purpose. GTM used for this purpose should have as low HAV as possible so as to avoid damage in terms of HAVS.