• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.167-174
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• 2010

In this study, the optimal position for the backrest pivot of an office chair was investigated by evaluating its performance in terms of the lumbar support and sliding distance of the back from the backrest during tilting motions. The simulation was performed using a mathematical model, which included a human body and a chair. Forty-two backrest pivot points were selected on the sagittal plane around the hip joint of a sitting model. A motion analysis study was also performed using a prototype of an office chair (A-type) with a backrest pivot located on the hip joint of a normal Korean model and a typical office chair (B-type) with its pivot located under the seat. The simulation results showed that both the lordosis angle and the slide distance of the back were minimized when the backrest pivot was positioned close to the hip joint. The experimental results showed that the slide distance and gap between the sitter's lumbar and the backrest was smaller with the A-type than the B-type. Based on the simulation and experimental results, it can be concluded that the backrest can support the sitter's lumbar area more effectively as the pivot position for reclining approaches closer to the hip joint. In this position, the sitter can maintain a comfortable and healthy sitting posture. This paper presents the methods and guidelines for designing an office chair with ergonomic considerations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.535-540
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• 2015

The location of the pivot between the backrest and seat pan of a reclining chair should be identical to the hip joint center to prevent unpleasant user experiences during tilting motion. However, mechanical friction occurs in the pin-in-slot joints that are installed under the seat pan as an alternative to the hinge joint. This reduces the reaction force between the backrest and the occupant's back when reclining and returning to an upright position, which causes the occupant's discomfort. In this study, bearings, rollers, and sliders were suggested as alternatives for the pin component, and the percentage of the reaction force on the backrest was measured while reclining the backrest and subsequently returning it to an upright position. The results show when bearings, rollers, and sliders were used for the pin-in-slot joint, the percentages of the reaction force were $59.7{\pm}10.3$, $47.2{\pm}13.6$, and $30.3{\pm}18.1$, respectively, indicating that the friction of the bearing was the lowest among the three pin components. Because the three alternatives have different manufacturing costs, synthetic judgment requires the consideration of not only mechanical friction but also user experience.