Asif M. Mughal and Kamran Iqbal
Sit-to-stand, biomechanical movement, LMI, optimal control, voluntary movement
Sit-to-stand (STS) movement is a mundane movement coordination task that involves regulating the musculoskeletal structure of the body through central nervous system (CNS) control mechanisms. STS is the subject of interest for a variety of scientific researchers and experimentalists due to its importance in daily life. In this paper, we use a four-link sagittal plane biomechanical model for affecting STS transfer through mixed control optimization techniques. Optimization through modern control techniques provides the ad- vantages of lower cost function value and robust performance. These techniques utilize the optimization parameters obtained from H2 and performance bounds obtained from H∞ algorithms. We design a control algorithm using mixed linear matrix inequalities (LMI) by combining H2 and H∞ optimizations for physiologically improved results compared to previous studies. We simulate the results to find an optimum value between two LMIs for lower torques and ground reaction forces (GRFs) during the STS task. Furthermore, centre of mass (CoM) and GRF profiles of biomechanical movement are optimized to meet experimental data of healthy subjects. LMI control synthesis for STS task using a biomechanical model provides a framework to analyse physiological variables (kinematic and kinetic variables of biomechanical STS movement) as control objectives and neural delays in the sensory paths. In this study, we develop a procedure to validate movement coordination problem of STS task using biomechanical model and optimal controller design. Our results demonstrate that the control theory framework with simple biomechanical models has wide applicability for studying human voluntary movement.
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