Introduction Use of hand-held vibrating tools like drill machines, polishing machines etc. are very common in unorganised sectors where users recurrently encounter occupational vibration. Vibrational energy is transmitted from the vibrating hand-tool to human body primarily through hand-arm and affects from early fatigue to irreversible hand injuries. In the present research, design modification of a hand-held stone-polishing tool was done from ergonomics and industrial design perspective to reduce transmission of vibration and improving usability.
Methods Data pertaining to demographic characteristics, body parts discomforts and other occupational health related issues was collected from the users (n=30, localised in and around Guwahati city, India) of hand-held stone-polishing tool after administering the standardised questionnaire. Working postures was evaluated using REBA (rapid entire body assessment) technique. During use of polishing tool, quantification of the exposure to vibration was performed for 15 workers in three different working conditions (polishing on floor, stair and vertical wall). Following brain storming, CAD model and thereafter mock-up and prototype were developed from the final concept. Field trial of the redesigned polishing machine was carried out involving real users.
Results Following analysis and interpretation of the responses against the questionnaire, it was found that workers had been exposed to a high level of hand-arm vibration, adopting awkward postures, performing strenuous repetitive activities for prolong duration which ultimately imposed adverse impact on occupational health. Measurement of vibration transmission (in terms of intensity) to the wrist of the user before and after design intervention showed significant reduction.
Discussion The stone polishing machine was redesigned considering anthropometric and biomechanical compatibility to reduce biomechanical stress associated with hand and arm of the operators. A supportive mechanism was provided to avoid sustained load holding during polishing to reduce hand-arm fatigue. Handle grip was coated with rubber as vibration dampening material to reduce the vibration transmission to arm. The modified design with better usability and aesthetic look was liked by the users. It was evident from their higher comparative ratings against the existing design.
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