Intelligent user-specific motion planning and control of lower-limb exoskeletons

Abstract

Recent strides in lower-limb exoskeleton development have significantly enhanced the potential for more effective rehabilitation and assistance for individuals with mobility impairments. Despite these advancements, the widespread adoption of exoskeletons demands improvements in both hardware and software design to enhance user comfort and safety. This doctoral research addresses this need by focusing on the implementation of personalized and safe locomotion patterns, addressing a critical shortfall in existing exoskeleton designs. To empower users with the ability to modify gait trajectories during walking, a novel adaptable gait trajectory shaping method is introduced, leveraging adaptable central pattern generators (ACPGs). These ACPGs are synchronized across various joints and dynamically updated in response to the physical interaction between the human and the robot. Expanding on this, a fusion of reinforcement learning and ACPGs is proposed, enabling the generation of user-specific locomotion trajectories. This innovative approach reads the user's physical human-robot interaction (pHRI) over time, facilitating the achievement of desired gait patterns, such as step length and walking velocity. Experimental validation on able-bodied individuals using the Indego lower-limb exoskeleton demonstrates the capability of refining exoskeleton gait trajectories in real-time. To elevate safety levels, an algorithm is introduced to assess postural stability during changes in exoskeleton trajectories governed by ACPGs. An extended model for the divergent component of motion (DCM) is tailored for multi-degree-of-freedom (DOF) exoskeletons. Leveraging this algorithm, the exoskeleton gains the ability to ensure postural stability and the viability of locomotion in pHRI by employing a DCM-based hip correction strategy to adjust the upper body position. The effectiveness of this intelligent controller for ensuring safe and stable locomotion is rigorously investigated through experimental studies conducted on the Indego lower-limb exoskeleton.