Reactive balance control of an active lower limb orthosis during perturbed walking

At present, gait assistance technologies are in constant development. Indeed, with the global ageing of world population and the increasing rate of deaths related to falls, there is an increasing need for locomotion assistance devices. Because lack of balance and walking impairments are among the most common causes leading to falls, more and more active lower limb orthoses are being commercialized to cope with gait disorders. In spite of the global demand, specific reactive balance assistance that can respond to unexpected perturbations is rarely the subject of research for such devices. Therefore, we worked on the adaptation of potential balance models for an implementation in a mid-level controller of a lower limb orthosis. First, we had to find a bio-inspired model describing efficiently the reactive balance behavior responses of lower limb joints during perturbed walking. We decided to go for a center of mass and a joints based kinematics model. Second, to assess the different performances and choose the most adapted model, we fitted the different models via a linear regression on experimental data and evaluated the different results. Based on the performances, we chose a model and a joint to act on, in order to test a model-based controller in a neuromuscular bipedal locomotion simulation with reduced reactive balance capacities. Via the model fitting, we confirmed the ability of a delayed center of mass feedback model to reconstruct deviated ankle joints in response to a sagittal perturbation for different speeds of walking and different amplitudes of perturbation at a discrete time instance. Moreover, the evaluated models gave us more insights about neuromuscular sensorimotor transformations underlying reactive balance behavior of lower limb joints. Finally, the neuromuscular model did not allow us to assess the efficiency of our model, to enhance reactive balance through simulation on a rigid body, due to input and optimisation constraints. By following a bio-inspired approach, we proposed a potential ankle joint orthosis controller providing the reactive balance assistance, which could be one of future key components in the rehabilitation area to reduce the increasing fall rates.