Wearable Sensor System for Human Dynamics Analysis

Abstract

In clinical applications the quantitative characterization of human kinematics and kinetics can be helpful for clinical doctors in monitoring patients’ recovery status; additionally, the quantitative results may help to strengthen confidence during their rehabilitation. The combination of 3D motion data obtained using an optical motion analysis system and ground reaction forces measured using a force plate has been successfully applied to perform human dynamics analysis (Stacoff et al., 2007; Yavuzer et al., 2008). However, the optical motion analysis method needs considerable workspace and high-speed graphic signal processing devices. Moreover, and if we use this analysis method in human kinetics analysis, the devices are expensive, while pre-calibration experiments and offline analysis of recorded pictures are especially complex and time-consuming. Therefore, these devices is limited to the laboratory research, and difficult to be used in daily life applications. Moreover, long-term, multi-step, and less restricted measurements in the study of gait evaluation are almost impossible when using the traditional methods, because a force plate can measure ground reaction force (GRF) during no more than a single stride, and the use of optical motion analysis is limited due to factors such as the limited mobility and line-ofsight of optical tracking equipment. Recently, many lower-cost and wearable sensor systems based to multi-sensor combinations including force sensitive resistors, inclinometers, goniometers, gyroscopes, and accelerometers have been proposed for triaxial joint angle measurement, joint moment and reaction force estimation, and muscle tension force calculation. As for researches of wearable GRF sensors, pressure sensors have been widely used to measure the distributed vertical component of GRF and analyze the loading pattern on soft tissue under the foot during gait (Faivre et al., 2004; Zhang et al., 2005), but in these systems the transverse component of GRF (friction forces) which is one of the main factors leading to fall were neglected. Some flexible force sensors designed using new materials such as silicon or polyimide and polydimethyl-siloxane have been proposed to measure the normal and transverse forces (Valdastri et al., 2005; Hwang et al., 2008), but force levels of these sensors using these expensive materials were limited to the measurements of small forces (about 50N). By mounting two common 6-axial force sensors beneath the front and rear boards of a special shoe, researchers have developed a instrumented shoe for ambulatory 8