Modeling and optimal control of twist and tilt biped for sit to stand

The construction of a rigid body biomechanical model with higher ordered controller design is a challenging task due to the complicated architecture and complexity of human intended movements. Biomechanical analysis of such complex model for sit-to-stand (STS) movement in three dimensions (3D) requires the envisioned actions of humans by utilizing motor controls. The current study aims to enhance our investigation into 3D bipedal mobility by creating optimal control for our novel Twist and Tilt foot mechanism. Unlike earlier models, this mechanism does not assume any fixed foot for the entire profile. This novel model type enables one foot to perform a twisting motion and the other foot to execute a sliding tilt motion. This technique simulates the control effort needed during the STS task by individuals with neurological impairments while performing various joint positions. The twist and tilt model is created using computer-aided design (CAD) software SOLIDWORKS, utilizing an 8-segment biped. The linearized model in SIMULINK generated 24th ordered State Space model. Subsequently, we developed LQR (linear quadratic regulator) controller for attaining the desired trajectories in MATLAB/SIMULINK. This novel twist and tilt optimal control strategy have improved angular profiles and simulation results showcase the stroke patient's movements with one foot sliding deficient tilt and other foot twisting during the profile.