Bioinspired preactivation reflex increases robustness of walking on rough terrain

Abstract

Walking on unknown and rough terrain is challenging for (bipedal) robots, while humans naturally cope with perturbations. Therefore, human strategies serve as an excellent inspiration to improve the robustness of robotic systems. Neuromusculoskeletal (NMS) models provide the necessary interface for the validation and transfer of human control strategies. Reflexes play a crucial part during normal locomotion and especially in the face of perturbations, and provide a simple, transferable, and bio-inspired control scheme. Current reflex-based NMS models are not robust to unexpected perturbations. Therefore, in this work, we propose a bio-inspired improvement of a widely used NMS walking model. In humans, different muscles show an increase in activation in anticipation of the landing at the end of the swing phase. This preactivation is not integrated in the used reflex-based walking model. We integrate this activation by adding an additional feedback loop and show that the landing is adapted and the robustness to unexpected step-down perturbations is markedly improved (from 3 to 10 cm). Scrutinizing the effect, we find that the stabilizing effect is caused by changed knee kinematics. Preactivation, therefore, acts as an accommodation strategy to cope with unexpected step-down perturbations, not requiring any detection of the perturbation. Our results indicate that such preactivation can potentially enable a bipedal system to react adequately to upcoming unexpected perturbations and is hence an effective adaptation of reflexes to cope with rough terrain. Preactivation can be ported to robots by leveraging the reflex-control scheme and improves the robustness to step-down perturbation without the need to detect the perturbation. Alternatively, the stabilizing mechanism can also be added in an anticipatory fashion by applying an additional knee torque to the contralateral knee.

Gait Compensation Strategies to Expected and Unexpected Yielding Terrain

“…The consistent patterns observed in these behaviours indicate that these strategies are in uenced by prior experiences, as previously observed by Patla 1 and supported by recent literature [17][18][19]21,22 . These ndings provide a valuable database for further investigations involving children and individuals with pathological conditions.…”

“…Different research groups have examined adaptation to uneven terrain through electromyography 19 and centre of mass analysis 20 . Furthermore, Bunz and colleagues employed a neuromusculoskeletal model to predict preactivation re exes during walking on rough terrain 21 , and Bucklin and colleagues studied adaptive behaviour during unpredictable lateral pelvis perturbations on a treadmill 22 . Taylor and colleagues described perturbation effects through treadmill manipulation, albeit with limited reporting of spatiotemporal parameters 23 .…”

Uneven Walking Momentum Regulation Exhibit Different Strategies based on Age and State of Lookahead

“…Additionally, older adults exhibit greater force-generating errors and larger force variability when producing knee extensor eccentric control [10]. Since it is needed to exert large forces to go atop the perturbation [9], the slowdown exacerbates the magnitude of the positive work performance required for older adults.…”

“…This strategy involves speeding up before the perturbation and maintaining speed modulation over multiple steps postperturbation. Additionally, the pre-activation reflexes can enhance a bipedal system's ability to respond to unexpected perturbations on rough terrain [10].…”