Ochae Kwon

Determination of key dimensions for a glove sizing system by analyzing the relationships between hand dimensions

The present study identified key dimensions for the development of a glove sizing system by analyzing the relationships between hand dimensions and demonstrated the construction process of glove sizing systems based on the selected key dimensions. Three hand dimensions (HL: hand length; HC: hand circumference; HB: hand breadth) were selected as the candidates of glove key dimensions by surveying the literature and industry practices of glove sizing systems. Of the key dimension candidates, HL and HC were selected by examining the results of correlation and multiple regression analyses on the 1988 US Army hand anthropometric data. A cross-tabulation of HL and HC with an interval length of 1.3 cm was constructed for each gender and the corresponding lengths and circumferences of cells covering more than 2% of the population were used to provide glove sizing parameters. It was identified that the glove sizing system for males is different from that for females and has more size categories.

Evaluation of the multivariate accommodation performance of the grid method

The present study examined the multivariate accommodation performance (MAP) of the grid method, a distributed representative human models (RHM) generation method, in the context of mens pants sizing system design. Using the 1988 US Army male anthropometric data and ± 2.5 cm of fitting tolerance, the grid method selected two key dimensions (waist girth and crotch height) out of 12 anthropometric dimensions and identified 25 RHMs to accommodate 95% of the population. The average MAP of the RHMs decreased dramatically as the number of anthropometric dimensions considered increased (99% for single dimension and 14% for 12 dimensions). A standardized regression model was established which explains the effects of two factors (sum of anthropometric dimension ranges; adjusted R(2) between key dimensions and other anthropometric dimensions) on the MAP of RHMs. This regression model can be used to prioritize anthropometric dimensions for efficient MAP improvement of mens pants design.

A Multivariate Evaluation Method for Representative Human Model Generation Methods: Application to Grid Method:

A small number of representative human models (RHMs) are used for efficient product design and evaluation in digital environments; however, the multivariate performance evaluation on existing RHM generation methods has not been made. The present study developed a multivariate accommodation evaluation method, and then applied the proposed method to evaluation of the grid method which generates RHMs at scattered grids over the population distribution. The measure multivariate accommodation performance quantifies the proportion of the population within representative grids formed to accommodate a designated percentage of the target population. Twelve RHMs were generated by the grid method to accommodate 95% of the 1988 US Army anthropometric database and it was found that the accommodation performance of the RHMs decreased dramatically as the number of anthropometric dimensions increased (accommodation percentage = 99% for a one dimension and 10% for 10 dimensions). Multiple regression analysis identified that three factors (overlap area of representative grids, adjusted R 2 between key dimensions and other body dimensions, and sum of body size ranges) significantly affect the accommodation percentage of the grid method. The proposed evaluation method is applicable for evaluation of other RHM generation methods.

Development of the boundary zone method for generation of representative human models

The present study developed a generation method of representative human models (RHMs) at a boundary zone which statistically accommodates a designated percentage of the target population. The boundary zone method proposed in the study consists of (1) identification of a boundary zone and (2) cluster analysis on cases within the identified boundary zone. The boundary zone of a designated accommodation percentage was formed by the normalized squared distance of each anthropometric case from the centroid of the target population. Cluster analysis was used to group homogenous cases within the boundary zone to reduce the number of the cases. A comprehensive evaluation under various combinations of anthropometric dimensions revealed that the average of multivariate accommodation percentages of the boundary zone method (91%) closer to the designated percentage (90%) than those of the existing generation methods (square method = 49%, circular method = 76%, and rectangular method = 96%).

Development of a Workload Assessment Model for Overhead Crane Operation

The operating tasks of overhead crane have caused undue stress to the operators from physical, mental, and environmental workload. Existing workload assessment models for musculoskeletal disorders such as OWAS, RULA, and QEC have limited applicability to the crane operating tasks because they focus mainly on physical factors and do not consider the relative importance of each factor. The present study was to develop a workload assessment model customized to overhead crane operation, following a systematic process: (1) analyzing task characteristics, (2) selecting workload factors, (3) developing assessment methods, (4) establishing action levels, and (5) computerizing the assessment model. Based on literature review, worksite survey, and focus group interview, 4 physical factors (awkward posture, static posture, repetitive motion, and excessive force), 6 mental factors (visual demand, auditory demand, task complexity and difficulty, time urgency, work schedule related stress, and safety related stress), and 4 environmental factors (noise, vibration, dust, and temperature) were selected and their rating scales and relative weights were determined. Then, based on the workload assessment results of 8 overhead cranes operated at different workplaces, the action levels of each factor category were established. Finally, the crane operation assessment model was computerized for effective analysis and report preparation. The present approach is applicable to develop a customized workload assessment model for an operating task under consideration.

Measurement and Application of 3D Ear Images For Earphone Design

Detail anthropometric dimensions and a 3D shape of the outer-ear are applicable to design ear-related products such as an earphone. However, 3D scanning of the ear part is quite difficult due to a complex shape of the ear, also detailed ear dimensions which are needed to be measured for earphone design were not identified in previous studies. This study collected 3D scan images of the whole outer-ear from 100 Korean participants (50 females and 50 males) aged 20 to 59, then measured their detailed ear dimensions for earphone design. The pinna part was directly 3D scanned; and complex shape of the concha and acoustic canal parts were cast by applying an ear casting tool, then the cast was scanned in 3D. 13 ear dimensions were measured by applying an ear measurement system coded using Matlab. Both 3D ear scans and ear measurements were applied to design some earphone parts (earphone-head, ear-band, ear-tip) in this study.

Development of HeadForms and an Anthropometric Sizing Analysis System for Head-Related Product Designs:

The present study developed a sizing analysis system based on the Civilian American and European Surface Anthropometry Resource (CAESAR) database of North Americans (n = 2,299) for head-related product designs. To find representative heads from a huge amount of 3D human scan database, a sizing analysis system is required for efficient analysis of sizing systems based on anthropometric measurements. The head of the CAESAR 3D scan were manually edited to improve a quality for better use to the product design. Twenty one anthropometric landmarks were marked on the edited 3D heads to measure 40 anthropometric dimensions related to the head product designs. All head and face dimensions were automatically measured by applying a measurement system coded using Matlab. Fifteen representative headforms were generated in terms of 5 ethnic groups (composite group, Caucasians, American Africans, Asians, and Hispanics) and 3 gender groups (composite gender, males, and females). Finally, the sizing analysis system was developed based on the measurement of the CAESAR for analysis of head and facial measurements and generation of sizing systems.

Evaluation of the FSA Hand Force Measurement System

The FSA (Force Sensitive Application) system measures hand force by using force resistance sensors. Compared to conventional hand force measurement systems such as Lafayette hand dynamometer and Jamar hydraulic hand dynamometer, the FSA system can be applied to analyze use of hand forces while the hand is manipulating objects for a task, However, the measurement performance of the FSA system has not been objectively evaluated. The present study tested the FSA system in terms of stability, repeatability, accuracy, and linearity at sensor (one sensor) and system (hand motions; power grip, pulp pinch, pulp press) level. In sensor level, the FSR sensor has good stability (CV ≤ 2%) and linearity (R 2=0.82), but has low repeatability (CV=11%~19%) and accuracy (22% of under evaluation on average). In system level, accuracy is dramatically worsened by increasing the number of sensors involved. For example, mean differences (MD) between the FSA and NK dynamometer are −0.09kgf, −1.15kgf, and −1.49kgf for pulp press (1 sensor), pulp pinch (2 sensors), and power grip (18 sensors). However, there is strong linear relationship between values from the FSA and NK dynamometer (R 2=0.82, 0.94, and 0.99 for pulp press, pulp pinch, and power grip). This performance result indicates that measurements from the FSA system should be used for relative comparison rather than for absolute comparison.

Structural Analysis and Practitioner Needs Survey for a WMSD Prevention Program

The KOSHA codes H-31 and H-30 provide general guidelines to establish a prevention program for work-related musculoskeletal disorders(WMSD). Understanding of the components and practitioner needs for a WMSD prevention program is necessary for effective revision and implementation of the KOSHA codes. The present study established a comprehensive structure for a WMSD prevention program and surveyed practitioner needs for the KOSHA codes. The comprehensive prevention program structure, consisting of 7 parts(organization, education, risk management, medical management, program evaluation, and record keeping) and 90 items, was constructed by analyzing WMSD prevention guidelines published by various government agencies such as KOSHA, OSHA and NIOSH. Next, 20 practitioners, from four industry sectors(auto manufacturing, auto part manufacturing, shipbuilding, and machinery), working in a safety and health department or labor union, were interviewed to collect opinions for the KOSHA codes in terms of relevance, government support, and additional information needed. Guidelines of the KOSHA codes requiring modifications and government supports were identified, which can be used to revise the KOSHA codes and to establish a government policy to promote the implementation of the KOSHA codes. Lastly, the survey revealed that integrated, customized, quantitative, and case information for WMSD prevention is additionally needed, which can be used as design guidelines for a WMSD prevention program manual for practitioners. Keyword: Musculoskeletal disorders, Prevention program, Ergonomic program, Practitioner needs, Ergonomic program manual

Anthropometric analysis of 3D ear scans of Koreans and Caucasians for ear product design

Abstract The present study measured 25 dimensions of the ear including the concha and ear canal for ergonomic design of ear products and compared with existing ear measurement studies. Scanning and casting methods were employed to produce 3D ear images for 230 Koreans and 96 Caucasians and measurements of the ear dimensions were obtained by identifying 21 landmarks on individual ear scan image. The Korean ear measurements were found significantly larger (mean difference  = 0.4–3.7 mm) and more varied (ratio of SDs =1.01–1.55) than those of Caucasians in most of ear dimensions. The average ear length and ear breadth of male were significantly longer ( = 1.3–7.0 mm) and wider ( = 0.8–3.0 mm) than those of female. Use of gender- and ethnicity-composite ear data is recommended in product design due to the much larger intra-population variations (7.5–22.2 mm) than the corresponding inter-population variations. Practitioner Summary: The 3D ear measurements of Koreans and Caucasians were collected and compared with those of different ethnic populations. The distinct ear features of the populations identified in this study are applicable to ergonomic design of ear products with better fit and comfort. Abbreviations: CCW: cavum concha width; CV: coefficient of variation; EB: ear breadth; EL: ear length; SD: standard deviation; SE: sampling error; 3D: 3 dimensional