An Ankle Exoskeleton Using a Lightweight Motor to Create High Power Assistance for Push-Off

Abstract

Active exoskeletons have capacity to provide biologically equivalent levels of joint mechanical power, but high mass of actuation units may lead to uncoordinated walking and extra metabolic consumption. Active exoskeletons normally supply assistance directly during push-off and have a power burst during push-off. Thus, the requirements on power of motors are high, which is the main reason for the high mass. However, in a muscle-tendon system, the strategy of injecting energy slowly and releasing quickly is utilized to obtain a higher peak power than that of muscle alone. Application of this strategy of peak power amplification in exoskeleton actuation might lead to reductions of input power and device mass. This paper presents an ankle exoskeleton which can accumulate the energy injected by a motor during the swing phase and mostly the stance phase and then release it quickly during push-off. An energy storage and release system was developed using a four-bar linkage clutch. In addition, evaluation experiments on the exoskeleton were carried out. Results show that the exoskeleton could provide a high power assistance with a low power motor and reduced the requirement on motor power by 4.73 times. Besides, when walking with the exoskeleton, the ankle peak power was reduced by 25.8% compared to the normal condition. The strategy which imitates the working pattern of the muscle-tendon system leads to a lightweight and effective exoskeleton actuation, and it also supplies ideas for the designs of lightweight actuators that work discontinuously in other conditions.

Review of control strategies for lower-limb exoskeletons to assist gait

“…In [ 300 ], the supply pressure of the pneumatic actuators is calculated so as to achieve a desired compliance (or equivalently, stiffness). In another study, a clutch is used to connect and disconnect a spring and a DC motor which is running during 85% of the gait cycle to stretch the spring, and is disengaged during the push-off period to let the spring release the stored energy and assist the ankle [ 178 ]. In a similar but simpler approach, a DC motor is used to compress a spring during stance (and this compression is also augmented by the dorsiflexion of the human ankle), and the stored energy is released at push-off [ 301 ].…”

“…Joint angles and angular velocities have also been used without the ground contact information to transition states [126,[178][179][180][181][182]. In [47], in addition to the angle and angular velocity of the knee joint, the moment at the joint and the angular velocity of the leg are involved in state transitioning.…”

“…Different states may only change the parameters and/ or inputs to a controller (for example [48,89,117,172,183,184]) or change the control strategy completely (for example [19,61,66,86,173,185,185]). It is also worth mentioning that sometimes the state machine does not involve any electronics, and is implemented using mechanical components only [164,178,179].…”

Design of a Passive Gait-based Ankle-foot Exoskeleton with Self-adaptive Capability

“…Driven by a winch actuator, the device converts the pulling force into a torque about the ankle joint [7,8]. Liu et al [9] proposed a lightweight exoskeleton with an elastic spring that can continuously store the energy injected by a lightweight motor, and release it quickly to provide high-powered assistance. To achieve linear motion, Meijneke et al [10] presented a series elastic actuator (SEA) consisting of an electric motor and a ball-screw gear to control the distance between two rigid endpoints on the shank and foot, respectively.…”

Sensors and Actuation Technologies in Exoskeletons: A Review

“…Trunk A1. Electric Actuation A1.a DC [ 106 ]; [ 118 ]; [ 170 ]; [ 217 ]; [ 138 ]; [ 119 ]; [ 154 ]; [ 25 ]; [ 59 ]; [ 131 ]; [ 141 ]; [ 244 ]; [ 219 ]; [ 79 ]; [ 180 ]; [ 182 ]; [ 184 ]; [ 221 ]; [ 186 ]; [ 223 ]; [ 194 ]; [ 241 ]; [ 124 ]; [ 137 ]; [ 136 ]; [ 227 ]; [ 151 ] ; [ 240 ] ; [ 89 ]; [ 200 ]; [ 232 ]; [ 101 ]; [ 78 ]; [ 233 ]; [ 145 ]; [ 143 ]; [ …”