Approximately 1.5 million senior citizens live under nursing supervision, and most require assistance with at least one or more Activities of Daily Living (ADL). These include transferring in and out of chairs, beds and toilets, which necessitates the ability to perform sit-to-stand transitions. The sit-to-stand transition is a complex full-body activity that requires the synergistic coordination of the upper and lower limbs and trunk. This paper presents a model-based control approach for an exoskeleton device that can provide assistance at the ankle, knee, and hip joints. Validation of the controller is based on simulations on a four-link model of the human body. The results show that the control strategy is successful for different sit-to-stand transition speeds, and when the user is providing only a part of the required torques or has a single weak joint. The results also demonstrate the effectiveness of the proposed control strategy in the presence of modeling error that provides further support for the robustness of this approach.

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