Joonho Hyeong

Development of Tilting Chair for Maintaining Working Position at Reclined Posture

Objective: The aim of this study is to develop an office chair enabling to keep working at reclined sitting posture. Background: Sedentary workers are supposed to change the posture frequently during long hours of sitting. A reclined sitting position has been recommended to reduce disc pressure. But slumped sitting posture caused by the buttock sliding forward without any adjustment of back reclining is commonly observed. The worker seems to have tendency to change the sitting posture maintaining working condition. We assumed the reason to be their hands movement away from the working space when tilting backward. Method: Slide mechanism allowing seat to move forward was designed to maintain the hand position in working space during reclining. A prototype was manufactured and tilting motion was analyzed using motion capture system. Four experiment chairs were tested including the manufactured prototype chair and three other commercial chairs. Results: A backward movements of the hand position were 13.0mm, 101.7mm, 156.1mm and 139.3mm at the prototype chair, compared to chair B, chair C and chair D, respectively. And the movement was remarkably small at the prototype chair. Conclusion: The developed seat sliding chair allows back tilting maintaining hand position at working space. We expect the user tilting back more often than normal tilting chair during seated work. But further investigation is required to figure out the effectiveness of the developed chair using prolonged working hours. Application: The developed office chair directly affects commercialization.

The Effects of Different Backrest Pivot Positions on the Human Body During Reclining of the Office Chair

초록:본논문에서는사무용의자의틸트동작시요추지지기능과등의미끄럼을평가함으로써등판회전중심의최적위치를연구하였다.이를위해인체와의자로이루어진수학적모델을이용하여틸트동작시뮬레이션을수행하였다.착석된인체모델의측면상에서고관절중심을포함한42개의위치에등판회전축위치를설정하고각각시뮬레이션을수행하였다.또한등판의회전중심이고관절에위치한의자시작품과좌판하부에위치한기존의의자에대해동작분석실험도함께수행하였다.시뮬레이션결과등판의회전중심이고관절중심에가까이위치할수록틸트시요추각도변화량과등의미끄럼거리는작아졌다.한편실험결과착석자의등과등판사이의이격변위와미끄럼변위는등판의회전중심이고관절위치에설계된시작품에서더작게측정되었다.시뮬레이션과실험결과로부터등판의회전중심이인체의고관절위치에가깝게설계되면틸트시착석자의요추를효과적으로지지해줄수있음을알수있었고이때착석자는보다편안하고건강한착석자세를유지할수있다.이결과는사무용의자에서등판회전축위치의인간공학적설계를위한가이드라인을제공한다.Abstract:Inthisstudy,theoptimalpositionforthebackrestpivotofanofficechairwasinvestigatedbyevaluatingitsperformanceintermsofthelumbarsupportandslidingdistanceofthebackfromthebackrestduringtiltingmotions.The simulation was performed using a mathematical model, which included a human body and a chair. Forty-twobackrestpivotpointswereselectedonthesagittalplanearoundthehipjointofasittingmodel.Amotionanalysisstudywasalsoperformedusingaprototypeofanofficechair(A-type)withabackrestpivotlocatedonthehipjointofanormalKoreanmodelandatypicalofficechair(B-type)withitspivotlocatedundertheseat.Thesimulationresultsshowedthatboththelordosisangleandtheslidedistanceofthebackwereminimizedwhenthebackrestpivotwas positionedclosetothe hipjoint. Theexperimental results showedthat theslidedistanceandgapbetweenthesitterslumbarandthebackrestwassmallerwiththeA-typethantheB-type.Basedonthesimulationandexperimentalresults,itcanbeconcludedthatthebackrestcansupportthesitterslumbarareamoreeffectivelyasthepivotpositionfor reclining approaches closer to the hip joint. In this position, the sitter can maintain a comfortable and healthysitting posture. This paper presents the methods and guidelines for designing an office chair with ergonomicconsiderations.

Sitting Posture Monitoring System Based on a Low-Cost Load Cell Using Machine Learning

Sitting posture monitoring systems (SPMSs) help assess the posture of a seated person in real-time and improve sitting posture. To date, SPMS studies reported have required many sensors mounted on the backrest plate and seat plate of a chair. The present study, therefore, developed a system that measures a total of six sitting postures including the posture that applied a load to the backrest plate, with four load cells mounted only on the seat plate. Various machine learning algorithms were applied to the body weight ratio measured by the developed SPMS to identify the method that most accurately classified the actual sitting posture of the seated person. After classifying the sitting postures using several classifiers, average and maximum classification rates of 97.20% and 97.94%, respectively, were obtained from nine subjects with a support vector machine using the radial basis function kernel; the results obtained by this classifier showed a statistically significant difference from the results of multiple classifications using other classifiers. The proposed SPMS was able to classify six sitting postures including the posture with loading on the backrest and showed the possibility of classifying the sitting posture even though the number of sensors is reduced.

A Trend Analysis of Dynamic Chair and Applied Technology

Objective: The objective of this study was to define the Dynamic Sitting (DS) through trend analysis and research on the Dynamic Chair (DC) and applied technologies. Background: The effects of changing posture on the human body have been studied to find out healthy sitting postures. It is believed that changing posture is effective in reducing disc pressure on spinal cord and preventing back pain and musculoskeletal disease. But, the definition of DS and trends of DC have not been researched yet. Therefore, trend analysis of DC and its applied technologies are required to define dynamic sitting posture. Method: We researched the type of occupant postures from previous studies. And then, sitting behaviors were classified into three types; (1) sitting and standing, (2) working and studying, (3) taking a rest. Results: Variety shapes of DC and applied technologies were found out. From the result, the trend of DC and applied technology were summarized from three perspectives. ; (1) changing the chair functions according to users intention, (2) conversion of dynamic chair technologies to office chair mechanism, (3) enables the user to change their sitting posture without operating control device. Conclusion: From this study, we defined dynamic sitting posture and analyzed the trend of DC and its applied technologies. This result might be used to develop an office chair for healthy sitting. But further investigation is required to figure out the technologies and functions for development of healthy chair. Application: The results of the publishing trend analysis might help to determine design concept of office chair.

Influence of folding mechanism of bicycles on their usability

In this study, foldable bicycles were evaluated in terms of their usability. Four types of folding mechanisms were identified depending on the number of pivots and the pivot axis direction: single lateral pivot (SLP), single vertical pivot, dual lateral pivot, and combined vertical-lateral pivot. Next, four bicycles-one each of these four types-were selected as test specimens. Ten subjects performed folding and unfolding tasks on each of these bicycles, and three-dimensional body motions and ground reaction forces were measured. The maximum trunk flexion angles and maximum increments in the ground reaction force were used as governing parameters for evaluating the comfort level for each bicycle type. The SLP type provided the lowest upper body flexion and ground reaction force and was hence judged to be the most comfortable folding system. Hence, a promising type of easily foldable bicycle was proposed, thereby encouraging its incorporation into public transit systems.

COMPARISON OF DYNAMIC STABILITY DURING WALKING AND RUNNING ON NONMOTORIZED CURVED TREADMILL ACCORDING TO CURVATURE RADIUS

It is generally believed that running on a curved surface is more unstable than running on a flat surface. In this study, the dynamic stability of locomotion on a nonmotorized curved treadmill (NMC...

Analysis of Functional Status and Determination for Improvement of ADLs: Korean Elderly

Muscular strength in the elderly is important factors deciding on functional state in daily lives, and functional state shows a health condition. Resistance training to prevent loss of muscle mass and muscle fiber atrophy due to aging can increase muscle mass and strength. Recently, resistance training to improve muscular strength and endurance has been actively researched. Resistance training increases activities of daily living and ability of the elderly, which makes healthy senescent. ADL/IADL is suitable for measuring health condition of the elderly. In this study, target muscles of resistance training were chosen through a correlation analysis between ADLs and elementary motion, and we presented a procedure to select target muscles and exercise equipments. This procedure consist of a survey method that were described detailed motion of ADL/IADL. So we should be to extract resistance training machine to improve functions of regarding fundamental motion. Result of study may improve daily life activities of the elderly through objectives and scientific approaches. Furthermore, it will be helpful to studies about various fields of the elderly.