Control Design for an Exoskeleton System Based on the Human Gait

Abstract

Abstract Exoskeleton systems are wearable devices originally designed to enhance the physical abilities of humans, and subsequently for medical rehabilitation purposes. Impedance control is primarily used to achieve adaptability in exoskeleton control research. The concept of motion balance has not yet been applied to exoskeleton systems, which led us to propose a digital-twin concept, which operates in parallel with the operator. The digital twin is calculated by analyzing the dynamic characteristics of the entire human body, with the aim of determining the joint torques required to maintain balance and stability. If a discrepancy is detected between operator movements and the torques calculated using the digital twin, the system promptly provides assistance to ensure the safe operation of the exoskeleton. This study implemented the digital twin by utilizing the MATLAB Simscape modeling tool to construct a bipedal robot model that conforms to human body proportions and simulates real human postures. The zero-moment point was used as a reference point in the model for the interaction forces between the bipedal robot and the ground. We adopted the cart-table model to simplify the gait balance control of the bipedal robot model. The controller outputs an assistive force at the position of the center of mass to maintain balance during walking. Finally, we converted the assistive force into ankle joint outputs to enhance gait stability and ensure that the waveform and numerical outputs were closer to real human data found in the literature.