| The study on human balance strategy is a major branch of human motion analysis. It is practically important in many fields, such as rehabilitation engineering, functional impairment diagnose, humanoid machine, sport science and so on. Using surface electromyography (sEMG) signals and via the method of combining experiment and theory analysis, the reaction strategy of human balance employed by both healthy persons and unilateral trans-femoral prosthesis (UTFP) users when they encounter an unexpected slip incident at the heel-contact moment during walking is investigated in this dissertation. The work was also extended to the application of the strategies to prosthesis design. The research work finished in this dissertation is divided into the following four aspects:1. Based on the analysis of gait parameters, e.g. the peak value of required coefficient of friction, the slip potential faced by UTFP users when walking on the normal surface, was compared with that of the healthy persons. It is found that 1) the UTFP users face greater slip potential than healthy persons; 2) the main reason for UTFP users to face greater slip potential is that both the unsymmetry of their gait and the body swing in the frontal plane are more serious than that of the control group; 3) the slip direction is entirely different when the slip occurred on the intact side and the prosthetic side, which is a main character in the slip gait of UTFP users.2. Via principal component analysis, feature extraction was performed on the sEMG signals which had been recorded from the muscles on legs and around waist of both healthy persons and UTFP users during slip events. Using the first principal component—"muscle power", the balance strategies which both healthy persons and UTFP users employed in slips were investigated in details. It is found that there are two steps of balance strategies in the slip events including"anti-slip"and"anti-fall", which is defined as two-step balance strategy. And the healthy persons can adopt both strategies in time during slips, while usually only one strategy can be performed for UTFP users. Besides, when slips occurr on the prosthetic side or the intact siderespectively, UTFP users would adopt entirely different strategies.3. Based on the principle of two-step balance strategy, the 2-D multi-rigid dynamical mathematical model of human body for slip gait was developed. With the assist of kinematical data and sEMG signals from gait experiments, the joint moments of healthy people were calculated and analyzed. The results indicate that the amplitudes of joint moments, the fluctuation of joint moments and the friction moments on joints increase significantly in slips.4. From the point of view that the amputee and the prosthesis constitute a man-machine system, the ways to improve the safety of UTFP users during walking on slippery condition are discussed preliminarily. Moreover, the principle of two-step balance strategy is applied to the design of new artificial knee joint with moment control function. The specimen prosthesis has achieved the original goal of improving gait performance and reducing the slip potential during the UTFP users walking on normal path.This work was financially supported by the National Natural Science Fund (NO. 30170242) and National Hi-Tech Research and Development (863) Program (NO. 2001AA320601). |
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