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Title: Development of an approach for interface pressure measurement and analysis for study of sitting
Authors: WU YAQUN
Keywords: Interface pressure,sitting, measurement
Issue Date: 5-Aug-2010
Citation: WU YAQUN (2010-08-05). Development of an approach for interface pressure measurement and analysis for study of sitting. ScholarBank@NUS Repository.
Abstract: Sitting is a common posture in daily lives. It has been extensively studied with respect to supporting surface, sitting posture, subject groups and other related aspects. The interface pressure between the human buttock and the supporting surface is an important metric which has been generally adopted for the evaluation of sitting-related issues. In order to provide a comprehensive view on the major issues of interface pressure, a complete process of the specific interface pressure data acquisition and methods of analysis as well as human testing experiments is presented. In this project, three kinds of interface pressure measurement sensors, consisting of Tekscan Flexiforce sensor, Body Pressure Measurement System (BPMS) and CONFORMat were compared in terms of measurement accuracy, drift and other sensing characteristics. Based on the comparison, the CONFORMat was selected for further characterisation. For CONFORMat, the triggering force threshold of crosstalk interference and inactive sensors were investigated for avoidance of such phenomena. In addition, the drift properties and measurement accuracy were evaluated and found to be acceptable. Preliminary sitting tests also showed satisfactory results with regard to the sensor performance for human subject experiment. Interface pressure analytical methods were developed for pre-processing of the pressure patterns to capture certain features of the pressure data. Firstly, a neighbourhood based thresholding method has been developed and found to be effective in removing outliers and reconstructing the voids in the pressure pattern. Secondly for the image registration, a new Particle Swarm Optimization (PSO) based registration method adopts the Hausdorff distance as indicator of the match between two pressure patterns. This method was verified to achieve more than 98% success rate in pressure pattern registration. The third method concerns pressure concentration which is harmful in sitting. The static pressure concentration can be identified by a threshold based method and dynamic pressure change can be recognized by a t-type test method. For a single-frame pressure pattern, the static pressure concentration is quantified by a pressure concentration rate whereby the concentrated area is also segmented. For multi-frame pressure sequence, the dynamic pressure change region can be identified by applying a t-type test to determine statistically significant changes. Lastly, a method for plotting the trajectory of centre-of-pressure (COP) and computing the COP movement range is introduced. COP is an important indicator for sitting stability and posture change. For testing of the pressure measurement hardware and the aforementioned analytical methods, subject testing was conducted. 12 subjects were recruited for three kinds of sitting: static sitting, side sitting and cross-legged sitting on both hard surface (HS) and a commercial cushion called ROHO. The results show that the ROHO cushion is efficient at removing pressure peaks compared with the hard surface. The study on the dynamic pressure change indicates that side sitting is beneficial for prolonged sitting as it can greatly reduce the concentrated pressure in the lifted leg area. When the COP trajectory and movement range of side sitting and cross-leg sitting were compared, the latter appeared to have a more consistent sitting posture with similar COP trajectories. Furthermore, cross-leg sitting on hard surface generates much smaller COP movement range compared to ROHO, which is usually related to better sitting stability.
Appears in Collections:Master's Theses (Open)

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