Design and control of a bio-inspired soft wearable robotic device for ankle–foot rehabilitation

Abstract

We describe the design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle-foot rehabilitation. The design is inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle-tendon-ligament structure. A key feature of the device is its soft structure that provides active assistance without restricting natural degrees of freedom at the ankle joint. Four pneumatic artificial muscles assist dorsiflexion and plantarflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait pattern analysis. For the subject tested, the prototype is capable of generating an ankle range of motion of 27° (14° dorsiflexion and 13° plantarflexion). The controllability of the system is experimentally demonstrated using a linear time-invariant (LTI) controller. The controller is found using an identified LTI model of the system, resulting from the interaction of the soft orthotic device with a human leg, and model-based classical control design techniques. The suitability of the proposed control strategy is demonstrated with several angle-reference following experiments.

Design, fabrication and control of soft robots

“…The result is soft actuators with reduced extensibility and flexibility, but the ability to withstand higher actuation pressures, and hence apply larger forces. Using complex molding and/or freeform fabrication techniques, it is possible to embed fibers directly into pneumatic elastomeric actuators to achieve agile motions based on bending 27,13,37 . While most soft robot prototypes have used pneumatic or hydraulic actuation, a great deal of research has focused on the development of electrically activated soft actuators composed of electroactive polymers (EAPs) 38,39 , which have also led to prototype systems 22 .…”

“…Recently, researchers have begun to look at medical wearable applications for soft robotics including soft wearable input devices (e.g. wearable keyboards 92 ), soft orthodics for human ankle-foot rehabilitation 37 , soft sensing suits for lower limb measurement 93 , soft actuated systems for gait rehabilitation of rodents who have had their spinal cord surgically cut 94 , and a soft system for simulation of cardiac actuation 95 .…”

Three-Dimensional Hysteresis Modeling of Robotic Artificial Muscles with Application to Shape Memory Alloy Actuators

“…McKibben actuators can convert energy from compressed air to mechanical motion [3,8]. Although they have been utilized in a variety of robotic applications [2,5,20], the accurate control of these actuators have proven to be difficult due to the friction-induced hysteresis [8]. Although static models have been derived, the complete hysteresis is often not explicitly captured [3,11,28].…”

A Preliminary Study on Robot-Assisted Ankle Rehabilitation for the Treatment of Drop Foot

“…With respect to traditional passive foot orthoses, these actuated devices have additional capabilities to promote appropriate gait dynamics for better rehabilitation The MIT Anklebot developed by Roy et al [20] was controlled to adjust the impedance of the orthotic joint throughout the walking cycle for the treatment of drop foot. Park et al [21] developed an active soft ankle orthotic device for use in treating ankle-foot pathologies associated with neuromuscular disorders, including drop foot. Ferris et al [19] constructed a powered ankle-foot orthosis for human gait rehabilitation with a novel myoelectric controller.…”