Seung-Min Mo

Evaluation of Main Factors Affecting on the Legibility of One-Syllable Korean Characters and Numbers

ABSTRACT The purpose of this study was to evaluate the legibility of on e-syllable Korean characters with the participation of sixteen subjects. The experiment considered nine factors including age (young and old), gender (male and female), illuminance (150lx and 600lx), viewing distance (50cm and 200cm), material type (paper and LCD), typeface (Ming and Gothic), thickness (plain and bold), color contrast (black letter/white background and white letter/black background), and complexity (simple, complex, and number) to examine main effects with a 2 6-3 ×3 fractional factorial design. The dependent variables were minimum character size of 100% correctness, maximum character size of 0% correctness, and minimum character size of comfortable reading preference. The results of analysis of variance (ANOVA) revealed that age, illuminance, viewing distance and complexity were significant for all dependent variables, except gender which was significant only for the minimum character size of comfortable reading preference. In general, the young could see twofold smaller size letters than the elderly. The subjects could see smaller sized letters with the illuminance of 600lx and viewing distance of 50cm than 150lx and 200cm, respectively and also with numbers, simple char acters, and complex characters in that order. The findings of this study could be characterized about the legibility of Ko rean characters and be good resources for developing its standar d. Keyword: Legibility, Korean, Legible ch aracter size, One-syllable, Number

Literature Review on One-Handed Manual Material Handling

By referring thirty-seven previous studies on manual material handling (MMH), this paper analyzed guidelines and main factors of one-handed tasks. The previous studies concerned main factors of distance, weight, frequency, posture, gender, age, training, direction of force, height of the force exerted, and object shape and size. Based on these factors, the criteria used to understand one-handed tasks were objective measures of maximum strength, reaction force, etc., psychophysical measures of maximum acceptable frequency and weight, etc., and physiological measures of oxygen uptake, heart rate, electromyography, etc. An allowance threshold model regarding quantitative and objective fatigue and workload would be suggested for future research. This study would be expected that it serve to establish and Korean recommendations of one-handed tasks.

Anthropometric Data for Biomechanical Hand Model

The aim of this study was to investigate the anthropometric data for the segment masses, center of mass (COMs) of the segments of inertia, and radii of gyration are required for the development of the biomechanical hand model. The segment masses were calculated on the basis of the segment volume using a density of 1.1 g/cm3. The segment volume was estimated from the measured length between the participants’ distal and proximal joints (segment length) and the diameters of their knuckles. The COMs for the proximal and middle segments and the distal segment were determined by approximating the phalanx by the frustum of a cone and a cylindrical homogeneous rigid body, respectively. The diameters of the knuckles were measured for each participant. We assume that they have a uniform density. The moments of inertia of the proximal and middle segments were determined by approximating the phalanx as the frustum of a conical homogenous rigid body. The diameters of the knuckles were measured for each participant. The moments of inertia of the distal segments were determined by approximating the phalanx as a cylindrical rigid body. The radii of gyration, Kx, Ky, and Kz, of the segment about the x axis, y axis, and z axis are defined as Pytel and Kiusalaas. This information will be provide useful data for development of biomechanical hand model.

The Evaluation of Lower-limb Muscular Fatigue during Walking on Industrial Grating Type

Industrial grating has been widely used the work surface of manufacturing, plants, and shipyards due to excellent drainage and durability. The purpose of this study is to evaluate the localized muscle fatigue in lower limb by the grating type during walking. Six subjects were male industrial workers who participated in this study. This study considered four independent variables which were grating type, bar type, spacing and muscle. Surface electromyography signals from tibialis anterior (TA), peroneus longus (PL), gastronemius medialis (GM), and gastrocnemius lateralis (GL) were recorded to determine muscle fatigue. To assess fatigue, mean power frequency (MPF) drop rate of each experimental condition was obtained by using initial MPF (the initial 10 second) and last MPF (the last 10 second) and defined by percent decrease. As a results of Friedman test, grating type showed statistically significant difference (p=0.0317). The MPF drop rate of steel grating analyzed significantly higher 1.5%p than top grating. There were not significantly differences in bar type (p=0.0758), spacing (p=0.7630), and muscle (p=0.2803). It means that top grating evaluated low muscle fatigue than steel grating. That is why top grating should be not only having higher walking stability but also psychological safety due to a firmly structure and less exposed under grating. This study could be recommended to ergonomic work surface by grating to improve walking stability and safety.

Dynamic Electromyography Analysis of Shoulder Muscles for One-handed Manual Material Handing

Objective: The objective of this research is to quantitatively analyze muscle activities of arm and shoulder, according to direction in various types of one-handed manual material handling, based on surface electromyography. Background: Workers in industrial sites frequently carry out one-handed manual material handling using arm and shoulder muscles. Therefore, chronic load and accumulated fatigue occur to arm and shoulder muscles, which becomes a main cause of upper arm and shoulder musculoskeletal disorder. The shoulder muscles have widely range of motion, and complex interactions take place among various muscles including rotator cuff muscles. In this regard, research on interactions among should muscles, according to such various dynamic motions, is required. Method: Ten male subjects in their 20s participated in this research. This research considered upward, downward, leftward, rightward, forward and backward directions and fourteen muscles around arm and shoulder (biceps brachii and trapezius, etc.) as independent variables. The mean muscle activity was set as the dependent variable. This research extracted 4th~7th repetition signals according to ten times of repetitive muscle contraction, and analyzed the muscle activity concerned using the envelope detection technique. Results: The mean muscle activity of upward direction was analyzed highly statistically significant. The reason is that the effect of gravity works to arm and shoulder muscles. Also, it is conjectured that deformation of coracoacromial ligament was caused, and its contact pressure increased, due mainly to the shoulder flexion, and therefore load was analyzed high. Muscle activity was analyzed significantly low, according to concentric ballistic motion used in the concentric contraction phase by storing elastic energy in the eccentric contraction phase with a motion to bring the weight to the front of subject’s body as to downward, leftward and backward directions. Because, elbow joint’s flexion-extension motions mainly occurred, biceps brachii was analyzed high muscle activity as the prime mover. Conclusion: The information on the quantitative load muscles can be applied to ergonomic work design for one-handed manual material handling to minimize muscle load. Application: This research has effectively identified muscle activity according to dynamic contraction by applying an envelope detection technique. The results can be used for ergonomic work design to minimize muscle load during the one-handed manual material handling, according to each direction. The research results are expected to be used for musculoskeletal disorder prevention and physiotherapy in the rehabilitation medical field, based on the muscle load of arm and shoulder in various directions.

Reproducibility of Electromyography Signal Amplitude during Repetitive Dynamic Contraction

Objective: The aim of this study is to evaluate the fluctuation of signal amplitude during repetitive dynamic contraction based on surface electromyography(EMG). Background: The most previous studies were considered isometric muscle contraction and they were difference to smoothing window length by moving average filter. In practical, the human movement is dynamic state. Dynamic EMG signal which indicated as the nonstationary pattern should be analyzed differently compared with the static EMG signal. Method: Ten male subjects participated in this experiment, and EMG signal was recorded by biceps brachii, anterior/posterior deltoid, and upper/lower trapezius muscles. The subject was performed to repetitive right horizontal lifting task during ten cycles. This study was considered three independent variables(muscle, amplitude processing technique, and smoothing window length) as the within-subject experimental design. This study was estimated muscular activation by means of the linear envelope technique(LE). The dependent variable was set coefficient of variation(CV) of LE for each cycle. Results: The ANOVA results showed that the main and interaction effects between the amplitude processing technique and smoothing window length were significant difference. The CV value of peak LE was higher than mean LE. According to increase the smoothing window length, this study shows that the CV trend of peak LE was decreased. However, the CV of mean LE was analyzed constant fluctuation trend regardless of the smoothing window length. Conclusion: Based on these results, we expected that using the mean LE and 300ms window length increased reproducibility and signal noise ratio during repetitive dynamic muscle contraction. Application: These results can be used to provide fundamental information for repetitive dynamic EMG signal processing.