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최협(Hyeob Choi),박수경(Sukyung Park) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
For modern people who sit for a long time in daily-lives, back pain is a critical disease. The back pain is closely related to bad posture, but there are limited systems to monitor sitting posture. Moreover, those systems have some shortcomings to be used in daily-lives. Wearing inertial measurement unit bothers the user’s natural movement and motion camera needs wide-open space. In this study, we proposed a method to estimate sitting posture based on ground reaction force that could be measured without wearing sensors or the need of large space. We modeled the upper-body as a multi-segment rigid body and developed several assumptions, and ten subjects participated in the sitting test with various postures to verify our model. The results showed sitting trunk angle could be reasonably estimated based on GRF under straight posture condition. It implies that the proposed method could be functionally suited as a posture monitoring system.
최협(Hyeob Choi),박수경(Sukyung Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Human uses various sensory signals in perceiving body movement. To percieve movement, the CNS uses signals with proper weighting, and this system can be changed by cognition and conditions of body, which is called 'sensory reweighting'. The purpose of study was examining sensory reweighting when human do not trust vision, and we quantified each sensory signal's weight. Ten healthy male volunteers were instructed that respond perception of movement direction on moving platform accelerated at 0.1㎐ with 2mG magnitude near threshold. Visual stimulus was consisted of headtracked visions and reversed visions, and they are randomly sequenced. In first experiment, subjects did not cognize that vision could be reversed, and subjects were aware of it in second experiment. Other signal's weights increased when subjects did not trust vision, but vision was still dominant sensory signal. The results imply that visiual cues are still dominant in motion perception although human do not trust vision.
병진운동 자극에서의 HMD 시간지연에 의한 멀미의 역치 고찰
이은강(Eun Kang Lee),최협(Hyeob Choi),김명섭(MyeongSub Kim),박준혁(Junhyeok Park),이용우(Yongwoo Yi),박수경(Sukyung Park) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Virtual reality (VR) related products are newly rising on electronics and entertainment market. Head Mounted Display (HMD) is one of the popular instrument to implement VR environment. However, HMD system has latency which is time delay between user’s motion and display. One of the reason for Motion Sickness (MS) or Simulator Sickness (SS) is known as sensory conflict and when there are more latency in HMD system, resultant sensory conflict will be greater. Therefore HMD manufacturers pursue less latency as possible, but at some point, it costs too much and if perceptional thresholds for latency exist, then amount of latency which is cost-efficient may exist too. Therefore in this study, we measured degree of MS as latency increases, under medial-lateral (ML) direction stimulus to find perceptional threshold of MS and SSQ (Simulator Sickness Questionnaire) was used to measure subjects’ MS/SS. Experiment 1 was done with 8 healthy male subject. Firstly we measured HMD system’s latency and added extra time delay to change latency condition from minimum to around 200 ms. Then sinusoidal motion stimulus with 0.25 Hz frequency and 1.23 m/s^2 peak acceleration was applied. Experiment 2 was done with 5 healthy male subjects and motion stimulus was changed to 0.32 Hz frequency and 2.0 m/s^2 acceleration, with ML movement in VR space is doubled and latency range increased to 400 ms. First experiment’s result did now show any meaningful changes in MS, but second experiment’s result had threshold-like increase in MS near 200~400 ms latency range. However, some subject had very low MS and did not show any changes in MS during experiment. This result may imply that for those are sensitive to MS, under ML directional motion stimulus, perceptional threshold exists around 200~400 ms latency. Also, for those are not sensitive to MS, latency had less or no effect on MS.