Switched observer based impedance control for an assistive robotic cart under unknown parameters

This paper presents a new control scheme of an assistive robotic cart that helps a user easily transport objects in various weights. The maneuverability of the cart would be highly affected by the loaded weight of the cart and the friction between the wheel and the floor. Our focus is placed on how to enable the cart to offer easy maneuverability by creating desired interactions with a user. For this, a switched observer based impedance control scheme is proposed to allow the cart to autonomously adapt to changes in the weight of the load and the friction. Specifically, a pre-determined impedance between the user and the cart is regulated to generate an assist force using the user´s input force and the velocity of the cart. The switched observer is designed to estimate the loaded weight and the friction coefficient for the precise computation of the amount of assistance. Further, using the process integration and design optimization approach, the observer gains are automatically adjusted, resulting in enhancing the control performance. We describe the proposed scheme in detail, and perform extensive simulations to demonstrate its effectiveness.