Human-in-the-loop optimization of hip assistance with a soft exosuit during walking

Abstract

Wearable robotic devices have been shown to substantially reduce the energy expenditure of human walking. However, response variance between participants for fixed control strategies can be high, leading to the hypothesis that individualized controllers could further improve walking economy. Recent studies on human-in-the-loop (HIL) control optimization have elucidated several practical challenges, such as long experimental protocols and low signal-to-noise ratios. Here, we used Bayesian optimization-an algorithm well suited to optimizing noisy performance signals with very limited data-to identify the peak and offset timing of hip extension assistance that minimizes the energy expenditure of walking with a textile-based wearable device. Optimal peak and offset timing were found over an average of 21.4 ± 1.0 min and reduced metabolic cost by 17.4 ± 3.2% compared with walking without the device (mean ± SEM), which represents an improvement of more than 60% on metabolic reduction compared with state-of-the-art devices that only assist hip extension. In addition, our results provide evidence for participant-specific metabolic distributions with respect to peak and offset timing and metabolic landscapes, lending support to the hypothesis that individualized control strategies can offer substantial benefits over fixed control strategies. These results also suggest that this method could have practical impact on improving the performance of wearable robotic devices.

Design and Control of a High-Torque and Highly Backdrivable Hybrid Soft Exoskeleton for Knee Injury Prevention During Squatting

“…The torque generated from the robot needs to be delivered at an angular velocity of no less than 2.4 rad/s to effectively synchronize with wearers. The robot is designed to deliver 72 Nm torque to provide more than 50% of biological lower limb joints as our control philosophy is to use small to medium levels of torque in combination with optimized timing, magnitude, and profile of torque trajectories [3]. Quasi-direct drive actuation [28] [29] is a new paradigm of robot actuation design that leverages high torque density motors with low ratio transmission mechanism.…”

“…The turnbuckles are a tensioner mechanism to apply pre-loading force to the cable transmission. Compared with [3] that use one motor to actuate a unidirectional motion, our mechanism uses one motor to generate bidirectional actuation, thus it can further reduce the mass of the overall system.…”

“…Pneumatic actuation operates on tethered air compressor [23], thus it is challenging for portable system applications. Textile soft exosuit is a new approach of soft wearable robot design and has been used for ankle [25] and hip joint [3] assistance during walking. There is no knee textile exosuit developed yet, possibly due to the demand to anchor wearable structures to thigh and shank while the ankle and hip exosuits can be anchored to footwear and waist respectively.…”

Rapid energy expenditure estimation for assisted and inclined loaded walking

“…Reducing this level of effort with gait retraining or assistance requires energy expenditure estimates to adapt the assistance to each user. Optimizing gait parameters and device assistance with "humanin-the-loop" methods has significantly reduced energy expenditure for steady state walking [4,5,6,7]. These methods rely on indirect calorimetry to estimate energy expenditure, which is expensive and provides noisy measurements after each breath [8].…”

From a biological template model to gait assistance with an exosuit

“…This feature is important in all above-mentioned cases and situations. 10 In the last couple of years researchers have succeeded in significantly improving the 11 metabolic cost reduction in human gaits using powered exoskeletons [1,[9][10][11].…”