Fuzzy Reduced Order Observer-Controller Design for Biomechanical Sit-to-Stand Movement

Successful execution of biomechanical sit-to-stand (STS) task combines a forward thrust phase with an upward extension phase and stable movement termination. We have previously developed a fuzzy dynamic model to analyze the STS task by joining two local linear models, defined at the equilibrium positions, via Gaussian membership functions. The local linear models were obtained from a four-segment biomechanical representation of the human body dynamics in the sagittal plane. Our fuzzy controller model uses an observer to reconstruct velocity data from noisy observation of joint positions. In this study, we propose a reduced order observer with an optimal controller design for the STS task. The fuzzy optimal controller generates feedback and feedforward components of joint torques, whereby the latter are derived from a reference trajectory. Our movement control strategy employing fuzzy reduced order observer with fuzzy controller leads to physiologically tractable simulation of the STS movement with results that are superior to those previously obtained with full order compensators.