A novel adaptive oscillators-based control for a powered multi-joint lower-limb orthosis

This paper introduces a novel control strategy for a multi-joint lower-limb exoskeleton during ground-level walking assistive tasks. It is aimed to define a physiologically consistent assistance to the human movements without engaging a complex sensory apparatus, hence providing a simple and comfortable human-robot interface. The control system is a two-block structure: one is based on adaptive oscillators (AOs) dedicated to the hip joint control, the other is a finite-state machine utilized for managing the assistive functions of knee and ankle joints. This control strategy was validated with two subjects walking on a treadmill wearing a hip-knee-ankle-foot (HKAF) exoskeleton. The tests were carried out at different speeds under both zero-torque and assistive control modes. Results presented repetitive and adaptive desired assistive torque profiles during all conditions and both subjects confirmed the benefits of gait assistance. We also analyzed the alterations of kinematics induced by assistive torques: the maximum-changed angle was 8.84 deg at ankle joint, and the time shifts of maximum/minimum angles were always lower than 2% of one stride cycle.