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Nonlinear control synthesis of biomechanical sit to stand movement

Sit-to-stand (STS) movement is a complex functional task which requires coordination of movement, postural regulation and stability for successful execution. STS transfer consolidates the highly nonlinear musculoskeletal structure together with neural control and tactile system in human body. In this paper we propose a nonlinear control technique based on feedback linearization to emulate the control action of central nervous system in performing STS movement. We use 4-segments rigid body biomechanical model with 3 degrees-of-freedom built on average anatomical proportions. In this controlling scheme, we adopt the output feedback computing through physiologically relevant optimization based upon center of mass (COM) and ground reaction forces (GRF). Furthermore, the output feedback provides passive control action commands including a linear quadratic regulator (LQR) based function augmented with nonlinear function computed with feedback linearization. The reference trajectories generate active feed forward torques, in addition with passive torques to settle the motion profiles within human anatomical constraints. The simulation results show that feedback linearization in combination with LQR provides an optimal frame work for better results of biomechanical STS movement as compared to previous linear control design schemes.