Ankle Exoskeleton Bowden Cable Torque Transmission
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Solution Overview
Problem
Designing effective lower-limb exoskeletons that can comfortably apply high torques at high bandwidth to assist gait while minimizing metabolic energy cost and interference with natural motion, and accommodating varying user anthropometry.
Innovation Solution
The development of ankle exoskeletons featuring a Bowden cable system, series elasticity, and modular design, which includes a shank portion with a strut and foot portion with a lever and pulley configuration, along with a load cell and motor controller to provide torque assistance and accommodate different user sizes through adjustable components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an ankle exoskeleton is placed on the leg to reduce metabolic energy cost, then metabolic energy cost is reduced, but it automatically incurs a metabolic energy penalty because it adds distal mass
Solution Approach 1:
The exoskeleton is divided into separate modular components including a shoe interface, ankle mechanism, and adjustable linkages. This segmentation allows the distal mass to be minimized by placing only essential components at the foot, while other components can be positioned higher up the leg where they add less metabolic penalty.
Solution Approach 2:
The exoskeleton employs adjustable linkages and modular components that can be reconfigured based on user needs. The adjustable ankle lever arm length and interchangeable components allow optimization of mass distribution dynamically, reducing distal mass when high torque is not required while maintaining capability when needed.
2Force
If the device applies large torques to assist ankle plantar flexion, then assistance effectiveness is improved, but the device complexity increases
Solution Approach 1:
The exoskeleton uses a pulley mechanism with a Bowden cable to generate torque, replacing complex motor-gearbox assemblies with a simpler cable-pulley system. The Bowden cable runs through a pulley attached to the ankle lever, providing smooth torque application with fewer moving parts and reduced mechanical complexity.
Solution Approach 2:
The Bowden cable acts as an intermediary mechanism between the actuation system and the ankle joint. It transmits force from a remote actuator through the pulley system to the ankle lever, simplifying the direct connection requirements and reducing mechanical complexity at the ankle joint itself.
3Use of energy by moving object
If the device width is reduced to decrease additional metabolic energy costs, then metabolic energy cost is reduced, but the ability to apply torque may be compromised
Solution Approach 1:
The exoskeleton utilizes the vertical dimension by positioning the pulley and Bowden cable arrangement above the ankle joint rather than expanding laterally. This allows torque application capability to be maintained through vertical placement of components, keeping the device width minimal and reducing metabolic energy costs associated with increased step width.
4Adaptability or versatility
If the exoskeleton is designed to accommodate varying user anthropometry through adjustability, then adaptability is improved, but device complexity increases
Solution Approach 1:
The exoskeleton features adjustable linkages with movable connection points and interchangeable components that allow customization to different user anthropometries. The adjustable ankle lever arm length and reconfigurable linkages provide adaptability without requiring completely different devices for different users, balancing complexity with versatility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The exoskeletons achieve robust torque tracking and comfortable interfacing, reducing metabolic energy cost and interference with natural motion, and can be adjusted to fit a range of users, demonstrating improved performance in assisting gait and reducing additional energy expenditure.
Implementation Method 1
The pulley is configured to redirect the Bowden cable back toward the shank portion, and wherein the Bowden cable is configured to generate torque by pulling the pulley
Implementation Method 2
Series elasticity improves torque control and decouples the human from the inertia of the motor and gearbox. The stiffness of the spring also determines the nominal behavior of the device
Data Source
AI summary
An exoskeleton device is disclosed. The exoskeleton device comprises a Bowden cable, a shank portion comprising a strut, and a foot portion coupled to the shank portion by a rotational joint. The foot portion comprises a heel lever and a pulley attached to the heel lever, wherein the strut of the shank portion is configured to redirect the Bowden cable toward the pulley, wherein the pulley is configured to redirect the Bowden cable back toward the shank portion, and wherein the Bowden cable is configured to generate torque by pulling the pulley. The exoskeleton device further comprises a midsole, wherein the midsole is releasably coupled to the lever, and wherein the midsole is configured to transmit force to a foot of a user.