Abstract
The growing field of soft wearable exosuits, is gradually gaining terrain and proposing new complementary solutions in assistive technology, with several advantages in terms of portability, kinematic transparency, ergonomics, and metabolic efficiency. Those are palatable benefits that can be exploited in several applications, ranging from strength and resistance augmentation in industrial scenarios, to assistance or rehabilitation for people with motor impairments. To be effective, however, an exosuit needs to synergistically work with the human and matching specific requirements in terms of both movements kinematics and dynamics: an accurate and timely intention-detection strategy is the paramount aspect which assume a fundamental importance for acceptance and usability of such technology. We previously proposed to tackle this challenge by means of a model-based myoelectric controller, treating the exosuit as an external muscular layer in parallel to the human biomechanics and as such, controlled by the same efferent motor commands of biological muscles. However, previous studies that used classical control methods, demonstrated that the level of device's intervention and effectiveness of task completion are not linearly related: therefore, using a newly implemented EMG-driven controller, we isolated and characterized the relationship between assistance magnitude and muscular benefits, with the goal to find a range of assistance which could make the controller versatile for both dynamic and static tasks. Ten healthy participants performed the experiment resembling functional daily activities living in separate assistance conditions: without the device's active support and with different levels of intervention by the exosuit. Higher assistance levels resulted in larger reductions in the activity of the muscles augmented by the suit actuation and a good performance in motion accuracy, despite involving a decrease of the movement velocities, with respect to the no assistance condition. Moreover, increasing torque magnitude by the exosuit resulted in a significant reduction in the biological torque at the elbow joint and in a progressive effective delay in the onset of muscular fatigue. Thus, contrarily to classical force and proportional myoelectric schemes, the implementation of an opportunely tailored EMG-driven model based controller affords to naturally match user's intention detection and provide an assistance level working symbiotically with the human biomechanics.
Highlights
The relatively novel frontier of soft wearable robotics and exosuits provided several solutions and tools potentially impacting multiple realms: from supporting people with neurological disorders, to improving labor efficiency in industrial settings by augmenting human motor capabilities
It is clear that different intervention levels of the exosuit do not dramatically change the kinematics of motion, showing that the controller effectively makes both the load and the hardware transparent to the user
Unlike the trend noted in the previous average rectified value (ARV) analysis, but confirming the result of postponing muscular fatigue, we found a positive progression in the median frequency (MNF) rate of change [F(3, 9) = 2.56, p = 0.05] across conditions: −0.21 ± 0.34, −0.48 ± 0.55, 0.10 ± 0.35, and 0.41 ± 0.43%/s in the no assisted (NE), LA, MA, and high assistive torque (HA), respectively, with a significant difference (p = 0.031) between HA and NE and (p = 0.019) between HA and LA
Summary
The relatively novel frontier of soft wearable robotics and exosuits provided several solutions and tools potentially impacting multiple realms: from supporting people with neurological disorders, to improving labor efficiency in industrial settings by augmenting human motor capabilities. The use of textiles and elastomers, intrinsically complying with the complex human biomechanics, has allowed a substantial leap in the rendering of Human-Robot interaction (HRI): explicitly in contrast with rigid exoskeletons, exosuits do not have the disadvantage of kinematic incompatibility with the human joints and they are designed with negligible distal mass on human limbs. These characteristics have allowed researchers and developers to reduce the energy cost of human walking and running (Kim et al, 2020) and support the upper limbs against gravity in both unimpaired users (Thalman et al, 2018) and neurological patients (O’Neill et al, 2020). While the rhythmic nature of human walking has allowed to exploit stereotypical gait events to recognize human intentions (e.g., Grimmer et al, 2019), upper limb dexterity, and its large tasks manifold, present a much more challenging and open problem
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