인간공학적 핸들 설계를 위한 손목 내전 및 외전에 따른 Power Grip 형상 변화 분석

Abstract

A handle, the part of an object for lifting, carrying, or controlling the object easily, needs to be ergonomically designed to prevent work-related musculoskeletal disorders of users. To recognize optimal handle design, previous studies evaluated applied forces, pressures, electromyograms (EMGs), and satisfactions with handles in various size and shape, and analyzed effect of hand size and grip posture. But most handle design dimensions in previous studies were limited to length variables of cylindrical handle and one grip posture. The present study is intended to analyze power grip deformation in hand dimension by wrist motion and propose the method of handle design related with hand dimensions. The proposed study consists of three steps: (1) understanding hand/handle dimension and analysis of hand-handle interface, (2) developing experiment protocol of hand grip deformation, (3) developing analysis protocol of hand grip deformation. First, in hand-handle interface analysis step, 40 handle related hand dimensions were chosen for measurement and analysis after understanding handle design dimensions and hand dimensions. Handle design dimensions of length, angle, and curvature were identified by dividing handle into 4 parts and using 16 reference points and 8 reference lines with shape of side, and cross section view. Handle related hand dimensions were chosen by checking the hand dimensions influence to decide handle dimension or not. For example, the width of handle was related with length of each finger’s tip to DTC/PTC. Finally, total 24 hand landmarks and 40 hand-handle dimensions were selected. Second, in experiment of hand deformation step, 15 participants (male 10, female 5) with 3 group of hand length was recruited and their hand grip postures were scanned by 3D scanner (3dMD). The 3 grip postures deformed by 3 handle orientation angles (65°, 45°, 15°) were selected to induce wrist adduction and abduction (20°, 0°, -30°). The elbow was controlled in 45° with elbow supporter. The 24 hand landmarks were marked to subjects’ hands with water-based pen. The outer hand shapes for each posture were scanned using 3dMD, and the inner hand shapes for each posture were molded using Otoform. Third, inner/outer hand 3D scan data were merged to body out full hand in grip posture and hand dimensions were measured based on hand landmarks. After 3D hand scan data were processed by modifying and aligning, inner and outer hand scan data were merged using Rapidform. The points of hand landmarks were created and hand dimensions of static posture and dynamic posture chosen by hand-handle interface analysis were measured and analyzed based on the points. The important measures of hand dimensions were tip to DTC/PTC and PIP to MMC in linear length, and tip to MMC in surface length which were related with handle width, thickness (height), and circumference. In addition, the measure of angle and curvature were measured by creating average curves fitted to inner hand. As a result, hand dimensions were significantly different by hand grip postures. When wrist angle was changed from neutral to adduction, tip to DTC/PTC (width) was increased 2.4% ~ 8.4%, PIP to MMC (height) was decreased 1.9% ~ 8.4%, and tip to MMC (circumference) was increased 2.8% in front part and decreased 3.6% in back part. When wrist angle was changed from neutral to abduction, tip to DTC/PTC (width) was increased 1.8% in front part and decreased 2.9% ~ 10.8% in back part, PIP to MMC (height) was increased 2.0% ~ 4.6% in front part and decreased 3.5% ~ 9.5% in back part, and tip to MMC (circumference) was decreased 0.1% ~ 6.3%. Also, the measures were decreased in ratio 64.7% ~ 73.9%, 43.1% ~ 54.4%, and 29.9% ~ 36.5% in comparison with static hand. If these results were applied to handle design, the thickness was increasing in front part and decreasing in back part when changing wrist adduction to abduction. The width was decreasing in all part and the circumference was decreasing in front part when changing wrist adduction to abduction.