Energy efficiency analysis and design optimization of an actuation system in a soft modular lower limb exoskeleton

One of the critical aspects in the design of an assistive wearable robot is the energy efficiency of the actuation system, since it affects significantly the weight and consequently the comfort of the system. Several strategies have been used in previous research, mostly based on energy harvesting, compliant elements for mechanical energy accumulation (springs or elastic cords), ratchets and clutches. However, the design of the optimal actuator arrangement is highly dependent on the task, which increases significantly the complexity of the design process. In this work we present an energy efficiency analysis and design optimization of an actuation system applied to a soft module lower limb exoskeleton. Instead of performing a comparison between predefined mechanism arrangements, we solve a full optimization problem which includes not only the mechanism parameters, but also the mechanism architecture itself. The optimization is performed for a walking task using gait data from a stroke subject, and the result is a set of actuator Arrangements with optimal parameters for the analyzed task and selected user. The optimized mechanism is able to reduce the energy requirements by 20-65%, depending of the joint. The proposed mechanism is currently under development within the XoSoft EU project, a modular soft lower-limb exoskeleton to assist People with mobility impairments

Back-Support Exoskeletons for Occupational Use: An Overview of Technological Advances and Trends

OCCUPATIONAL APPLICATIONSMany new occupational back-support exoskeletons have been developed in the past few years both as research prototypes and as commercial products. These devices are intended..

Basic functionality of a prototype wearable assistive soft exoskeleton for people with gait impairments : a case study

XoSoft is a soft modular wearable assistive exoskeleton for peo- ple with mild to moderate gait impairments. It is currently being developed by a European Consortium (www.xosoft.eu) and aims to provide tailored and active lower limb support during ambu- lation. During development, user-centered design principles were followed in parallel with the aim of providing functional support during gait. A prototype was developed and was tested for practi- cability, usability, comfort and assistive function (summarized as basic functionality) with a potential end user. The prototype con- sisted of a garment, electromagnetic clutch-controlled elastic bands supporting knee- and hip flexion and a backpack containing the sensor and actuator control of the system. The participant had ex- perienced a stroke and presented with unilateral impairment of the lower and upper extremities. In testing, he donned and doffed the prototype independently as far as possible, and performed walk- ing trials with the system in both active (powered on) and pas- sive (powered off) modes. Afterwards, the participant rated the perceived pressure and various elements of usability. Results high- lighted aspects of the system for improvement during future phases of XoSoft development, and also identified useful aspects of proto- type design to be maintained. The basic functionality of XoSoft could be assumed as satisfactory given that it was the first version of a working prototype. The study highlights the benefits of this participatory evaluation design approach in assistive soft robotics development

Enhancing Occupational Back-Support Exoskeletons Versatility

In the 1970s, the scientific community began addressing the relationship between musculoskeletal disorders (MSDs) and work ergonomics. Since then, many studies have been published regarding this topic. Yet, 50 years later, MSDs are still cited as the most common work-related health problem, in the majority of the cases due to back pain. Workers performing manual material handling (MMH) activities (e.g., package loading and unloading in a warehouse or luggage handling in airports) are among the most exposed to risks and injuries. Several solutions have been proposed but, due to high implementation costs or lack of acceptability by the workers, MSD problem has not been solved. Occupational back-support exoskeletons have been investigated for their ability to reduce muscle activation and, hence, mitigate the risk of injuries. Exoskeletons can be categorized as soft or rigid, if how the assistance is delivered to the user is taken into account, or as active, passive or quasi- passive, if, instead, focus is on the actuators that generate the assistance. Regardless of the categories, exoskeletons have been designed and tested, mostly, for static bending or lifting tasks. This is justified by the high risk of developing injuries associated with these tasks, but, on the other hand, does not address the complexity that out-of-the-lab environments might present. In this regard, an interesting study reported that if passive exoskeletons are used in non-lifting tasks, as walking, rather than helping they actually hinder and obstacle the wearers\u2019 movements. And, it is clear, that in industrial settings, workers do not lift for the whole duration of their schedule. Other relevant activities might be pushing, pulling or carrying. Indeed, the International Standard ISO 11228 establishes ergonomic guidelines also for these activities, highlighting that they could yield risk of injuries. Therefore, designing exoskeletons that address also these activities might help promote the acceptability of these devices. In this work, exoskeleton versatility is defined as the device ability to recognize which activity the user is performing and provide assistance accordingly. As an example, assisting with lifting could require the design of strategies that are not fit for carrying assistance. More in details, in the first part of this thesis, it is shown that considering spinal loading, carrying has an impact comparable to that of lifting. However, if lifting control strategies are used to assist with carrying, this produces gait impairments. The need of assisting with these two activities in different ways requires, first of all, a mean to recognize which task is taking place. This is addressed in the second part of the thesis. In particular, by using Support Vector Machines (SVM), it is shown that it is possible to build an automatic Human Activity Recognition (HAR) algorithm. Moreover, this algorithm can be embedded in the control architecture of XoTrunk, the back-support exoskeleton developed at our lab, enhancing its versatility. The third and last part of this this work assesses the advantages of using a versatile exoskeleton, comparing its performance to state-of-the-art exoskeletons and control strategies. At the end of the work, it is described the impact that exoskeleton versatility had on field testing

Dynamic and Static Assistive Strategies for a Tailored Occupational Back-Support Exoskeleton: Assessment on Real Tasks Carried Out by Railway Workers

This study on occupational back-support exoskeletons performs a laboratory evaluation of realistic tasks with expert workers from the railway sector. Workers performed both a static task and a dynamic task, each involving manual material handling (MMH) and manipulating loads of 20 kg, in three conditions: without an exoskeleton, with a commercially available passive exoskeleton (Laevo v2.56), and with the StreamEXO, an active back-support exoskeleton developed by our institute. Two control strategies were defined, one for dynamic tasks and one for static tasks, with the latter determining the upper body’s gravity compensation through the Model-based Gravity Compensation (MB-Grav) approach. This work presents a comparative assessment of the performance of active back support exoskeletons versus passive exoskeletons when trialled in relevant and realistic tasks. After a lab characterization of the MB-Grav strategy, the experimental assessment compared two back-support exoskeletons, one active and one passive. The results showed that while both devices were able to reduce back muscle activation, the benefits of the active device were triple those of the passive system regarding back muscle activation (26% and 33% against 9% and 11%, respectively), while the passive exoskeleton hindered trunk mobility more than the active mechanism

Soft Smart Garments for Lower Limb Joint Position Analysis

Revealing human movement requires lightweight, flexible systems capable of detecting mechanical parameters (like strain and pressure) while being worn comfortably by the user, and not interfering with his/her activity. In this work we address such multifaceted challenge with the development of smart garments for lower limb motion detection, like a textile kneepad and anklet in which soft sensors and readout electronics are embedded for retrieving movement of the specific joint. Stretchable capacitive sensors with a three-electrode configuration are built combining conductive textiles and elastomeric layers, and distributed around knee and ankle. Results show an excellent behavior in the ~30% strain range, hence the correlation between sensors’ responses and the optically tracked Euler angles is allowed for basic lower limb movements. Bending during knee flexion/extension is detected, and it is discriminated from any external contact by implementing in real time a low computational algorithm. The smart anklet is designed to address joint motion detection in and off the sagittal plane. Ankle dorsi/plantar flexion, adduction/abduction, and rotation are retrieved. Both knee and ankle smart garments show a high accuracy in movement detection, with a RMSE less than 4° in the worst case