Ergonomic investigations on hand arm vibration of brush cutter for the development of a vibration reducing aid

Abstract

Brush cutters are widely used in Kerala for weeding and clearing fields. While operating brush cutters, certain amount of vibration is transmitted to human body. Extended exposure to mechanical vibration can induce degeneration of the vascular and sensio-neural systems in the hand called hand-arm vibration syndrome (HAVS). The hand-arm vibration syndrome (HAVS) is a complex condition associated with vibration exposure and the use of hand-held vibrating machines. The vibration exposure of worker can be decreased by proper selection and maintenance of tool. To study the ergonomic aspects and hand transmitted vibrations of brush cutters, six subjects (3 male & 3 female) were selected who are having experience in operation of brush cutter. A suitable vibration reducing aid for brush cutters is designed and fabricated keeping the view that it should be capable of transmitting at least a part of the vibration produced at cutter head to the ground. It should be easily attached or detached from the brush cutters shaft. The material used for the vibration reduction aid should be light in weight and sturdy, so that it could be raised along with the cutter head by the operator. According to the conceptual design, a vibration reduction aid is developed and field tested. It consists of parts viz. curved arms, fixture to arms, quick fixing locks, ground rollers, rollers fixture and rubber grip. The brush cutter and vibration reducing aid is evaluated in the field with different cutter heads viz. nylon rope, 2 blade, 3 blade and circular blade. The experiment is repeated for 2-stroke and 4-stroke models of brush cutters operated by male and female subjects. The energy expenditure for brush cutter operation is calculated for two models of brush cutter for all subjects and compared. A statistical analysis is conducted using MSTAT software and found that the developed vibration reducing aid, blade and type of internal combustion engine have significant effect on vibration excitation in both right and left handles of brush cutters selected. The proposed method of evaluating occupational risk related to mechanical vibration exposure while working with brush cutter makes it possibleto account the effect of attachment, cutter head and type of internal combustion engine. Subjective ratings like ODR, OER, OSR and BPDS also indicated significant effect of reducing vibration due to the vibration reducing aid.