The Roles of Shape and Size in the Pinch Effort of Screw Knobs Poh Kiat Ng 1,a , Qiao Hui Boon 1,b , Ka Xuan Chai 1,c , Shiong Lung Leh 1,d , Meng Chauw Bee 1,e and Adi Saptari 2,f 1 Faculty of Engineering and Technology, Multimedia University, Malacca, Malaysia 2 Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Malacca, Malaysia a pkng@mmu.edu.my, b qiaohui07@gmail.com, c ka_xuan_1990@hotmail.com, d ivanleh@live.com, e charles_bee28@hotmail.com, f adi@utem.edu.my Keywords: Shape, Size, Pinch effort, Pinch grip, Grip force, Ergonomics, Screw knobs Abstract. The most common body parts that sustain injuries at the workplace are the hands and fingers. In association to this, researchers have conducted various studies on grip span, forces, postures, contact area and strength. However, it appears that limited studies have been done on the design of screw knobs of ergonomic shapes and sizes for pinch grip activities. Thus, the aim of this study is to design, develop and assess screw knobs of ergonomic shapes and sizes for pinching activities. Several designs of screw knobs were designed and fabricated. The assessment of the knobs involved workers from a manufacturing firm. The ratings on the efforts to pinch and turn the knobs were collected using surveys and analyzed with reliability and descriptive and analyses. The results show that the workers mostly preferred using the small 5-lobes knob. However, the large ball knob was the least preferred knob to be used. The findings of this study can be used to create design guidelines on knob shapes and sizes to develop safer, more ergonomic and efficient knobs. Introduction In manufacturing firms, it was found that there is an average of 25 hand injuries occurring each year for every 10,000 workers [1]. It was also reported that the most common body parts that sustain injuries at the workplace are the hands and fingers [2]. In association to this, many researchers have looked into possible solutions such as ergonomic hand tools that can reduce unnecessary strain in the muscles [3-5]. There have also been many reviews and studies conducted on handle shapes, handle sizes, grip span, contact area, strength, postures, torque directions, pinch techniques and pinch force [6-18]. However, there appears to be limited studies concerning the design of screw knobs of ergonomic shapes and sizes, along with their implications to pinch grip activities. Therefore, this study aims to design and develop screw knobs of ergonomics shapes and sizes for pinching activities. The findings of this study can be used to create design guidelines on knob shapes and sizes for pinching activities. These guidelines can be used to develop safer, more ergonomic and efficient knobs. Shape and Size The shape of a pinched object may cause a change in the way the object is pinched [14]. The shape of the object also affects its handling properties [19]. According to Yuan and Kuo [19], ball shaped objects have better handling properties compared to oval shaped and cylindrical shaped objects because ball shaped objects provide natural handling properties for the human hand. Size can refer to how large or small an object is [20]. Kumar [21] suggests that the size of most objects is designed to vary depending on gender. Based on the hand size of various individuals, it is posited that a tool grip span should be designed in a position which can maximize one’s handgrip strength [21]. As the gripping/pinching diameter of the gripped/pinched object changes, the hand torque also changes [21]. Applied Mechanics and Materials Vols. 465-466 (2014) pp 1202-1206 Online available since 2013/Dec/19 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.465-466.1202 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 60.48.46.147-03/01/14,15:43:56)