Design of a Low Profile, Unpowered Ankle Exoskeleton That Fits Under Clothes: Overcoming Practical Barriers to Widespread Societal Adoption

Abstract

Here we present the design of a novel unpowered ankle exoskeleton that is low profile, lightweight, quiet, low cost to manufacture, intrinsically adapts to different walking speeds, and does not restrict non-sagittal joint motion; while still providing assistive ankle torque that can reduce demands on the biological calf musculature. This work is an extension of the previouslysuccessful ankle exoskeleton concept by Collins, Wiggin, and Sawicki. We created a device that blends the torque assistance of the prior exoskeleton with the form-factor benefits of clothing. Our design integrates a low profile under-the-foot clutch and a soft conformal shank interface, coupled by an ankle assistance spring that operates in parallel with the user's calf muscles. We fabricated and characterized technical performance of a prototype through benchtop testing and then validated device functionality in two gait analysis case studies. To our knowledge, this is the first ankle plantarflexion assistance exoskeleton that could be feasibly worn under typical daily clothing, without restricting ankle motion, and without components protruding substantially from the shoe, leg, waist or back. Our new design highlights the potential for performance-enhancing exoskeletons that are inexpensive, unobtrusive, and can be used on a wide scale to benefit a broad range of individuals throughout society, such as the elderly, individuals with impaired plantarflexor muscle strength, or recreational users. In summary, this work demonstrates how an unpowered ankle exoskeleton could be redesigned to more seamlessly integrate into daily life, while still providing performance benefits for common locomotion tasks.

Characterizing the comfort limits of forces applied to the shoulders, thigh and shank to inform exosuit design

“…Exosuits (soft exoskeletons) are wearable devices made primarily from soft/flexible structures that physically augment, assist, or enhance human movement or posture. Exosuits offer exciting potential to enhance human health and performance [1][2][3][4][5] with both passive and powered implementations, and applications in medical, military, and industrial domains. However, one of the most challenging aspects of exosuit design-as well as design for many other wearable assistive devices, from prostheses to rigid exoskeletons-involves the physical interfaces that connect the device to the person [1], [6][7][8].…”

Development of an Unpowered Energy Recycling Exoskeleton for Walking Assist

“…The EMG results demonstrated its good walking assistance effect. For the torsion 1, the peak and average EMG-values of soleus muscles dropped about 13% and 8% respectively, and that of gastrocnemius muscles dropped about 12% and 13% respectively compared to the results of control, so the walking assistance effect of this kind of exoskeleton is close to Matthew B. Yandells' work which has an average EMG-values reduction of 17% of soleus muscles [3]. We found that the relationship between the assist effect and spring stiffness is not simply linear, as shown in Fig.…”

“…Our main innovative point is that we make the assist process more in line with the foot force habit of human walking. Most of the unpowered walking assist exoskeletons set the force assist point on the heel to provide torque for ankle joint in the push-off phase while the heel is not subjected to force in push-off phase during normal walking [1,3,7,19]. So this design is easier for wearers to adapt to.…”

“…[20] Marc Doumit& Leclair, J. [7] Karl E. Zelik & Matthew B. Yandell [3] Total Mass 816-1006 g 4660 g 1350 g 459 g…”

“…The improvement of the walking economy could thus be bene cial for both healthy individuals and those with reduced mobility [2]. Many attempts have been made to assist walking especially unpowered assistive devices have demonstrated the capacity to capture and release energy throughout the gait cycle, and have shown the ability to achieve a net reduction in energy consumption [3,4].…”