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AnkleBot

The Anklebot is an exoskeletal robotic system using the same design principles that have made InMotion Robots. Ankle is an amalgam of physical and biological principles.

 

http://interactive-motion.com/wp-content/uploads/2013/07/AnkleBotEversion-Inversion-300x223.jpg

Anyone who has ever suffered an ankle injury will tell you how painful it was and how annoying the recovery was. To mitigate the aforementioned recovery time,  a robot that attaches to a knee brace and connects to a customized shoe called anklebot is designed. When the patient tries to move an ankle, the robot moves the foot along a predetermined trajectory, within the ankle’s normal range of motion. The robot records the angular displacement and torque of the joint, calculates the ankle’s stiffness, builds strength and redevelop muscle memory. The device has the ability to back off its intensity when the patient begins to move the ankle on their own

The ankle is critical for propulsion during walking and for balance and is also important in gait for the role it plays in “shock absorption” due to foot placement, furthermore studies have shown that ankle stiffness is modulated to accommodate surface changes during locomotion. Following stroke, “drop foot” is a common lower extremity impairment. It is caused by a weakness in the dorsiflexor muscles that lift the foot. Two major complications of drop foot are slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe swing). In addition to inadequate dorsiflexion (“toe-up”), the paretic ankle also suffers from excessive inversion (heel toward midline). This begins in the swing phase and results in toe contact (as opposed to heel contact) and lateral instability in stance.


Conventional passive ankle braces can improve gait, but long-term use can lead to muscle atrophy because of disuse. Active, powered devices can improve function and also help re-educate the neuromuscular system. The limitation of a traditional exoskeleton is that it limits the natural degrees of freedom of the body. The ankle is naturally capable of a complicated three-dimensional motion, but most rigid exoskeletons allow only a single pivot point. Anklebot allows 3D motion.

The AnkleBot can deliver a continuous net torque of ~23 Nm in dorsi-plantarflexion and 15 Nm in eversion-inversion.
The exoskeletal robot can estimate ankle angles with an error less than 1° in both planes of movement (maximum 1.5°) over a wide range of movement (60° in dorsi-plantarflexion and 40° in eversion-inversion) and can measure ankle torques with an error less than 1 N·m.


It has low friction (0.744 N·m) and inertia (0.8 kg per actuator for a total of 1.6 kg at the foot) to maximize the backdriveability.


https://www.youtube.com/watch?v=-JSnWSHaDUs#t=57