Artificial Ankle Foot System with Variable Damping and Series-Elastic Actuator
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Solution Overview
Problem
Current artificial ankle-foot systems fail to replicate the dynamic biomechanical behaviors of a human ankle, particularly in terms of varying stiffness, motive power, and damping, which are essential for natural locomotion and adaptation to different terrains and walking speeds.
Innovation Solution
The development of an artificial ankle system incorporating passive springs, series-elastic actuators, and variable dampers, along with a controller, to mimic the human ankle's behavior by storing and releasing energy and adjusting impedance during various phases of the gait cycle, including level ground walking and stair descent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If passive springs and series-elastic actuators are added to store and release energy, then the system can better mimic human ankle behavior and provide motive power, but the device complexity increases
Solution Approach 1:
The patent implements dynamic behavior through passive springs that automatically store and release energy during the gait cycle, and series-elastic actuators that provide adaptive stiffness control. These components dynamically respond to loading conditions without requiring active control systems, thereby achieving biomimetic behavior while managing complexity through passive mechanical design.
Solution Approach 2:
The passive spring mechanism serves itself by automatically storing energy during dorsiflexion and releasing it during plantarflexion without external control. This self-service capability eliminates the need for complex active control systems while achieving the desired motive power and energy storage functions.
2Adaptability or versatility
If variable dampers are incorporated to control damping during gait cycle, then the system can better absorb impact energies and mimic human ankle behavior, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent achieves variable damping control by changing the damping parameter through the natural variation of joint velocity during the gait cycle. The damper coefficient is adjusted passively based on the loading rate and joint angular velocity, eliminating the need for complex active control mechanisms while achieving impact energy absorption.
3Adaptability or versatility
If multiple actuators and springs are added to provide active control of stiffness and motive power, then the system can better replicate human ankle function, but the weight of the system increases
Solution Approach 1:
The patent segments the ankle-foot system into distinct functional components: passive springs for energy storage, series-elastic actuators for stiffness control, and dampers for impact absorption. Each component is optimized independently, allowing the system to achieve active control capability while minimizing overall weight through targeted component placement and sizing.
4Productivity
If the system actively controls joint stiffness and damping to mimic human ankle behavior, then the operational performance improves, but the energy consumption increases
Solution Approach 1:
The patent utilizes periodic action by synchronizing energy storage and release with the natural gait cycle. Passive springs store energy during the stance phase and release it during swing phase, while series-elastic actuators provide periodic stiffness modulation. This periodic operation aligns with biological rhythms, maximizing locomotion efficiency while minimizing energy consumption through passive energy recovery.
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 system achieves biologically-realistic dynamic behaviors, providing efficient, high cycle-life, quiet, and cosmetic performance by actively controlling joint stiffness, damping, and motive power, thus enhancing the functionality and comfort of prosthetic and orthotic devices.
Implementation Method 1
The artificial system must be capable of varying its position, impedance, and motive power in a comparable manner to that of a normal, healthy biological limb... the ankle behaves as a variable stiffness device during the early to midstance period, storing and releasing impact energies
Implementation Method 2
for stair descent, the ankle behaves as a variable damper during the first half of stance, absorbing impact energies
Implementation Method 3
Throughout terminal stance, the ankle acts as a torque source to power the body forward... stiffness, damping, and nonconservative, motive power must be actively controlled
Data Source
AI summary
An artificial foot and ankle joint consists of a curved leaf spring foot member having a heel extremity and a toe extremity, and a flexible elastic ankle member that connects the foot member for rotation at the ankle joint. An actuator motor applies torque to the ankle joint to orient the foot when it is not in contact with the support surface and to store energy in a catapult spring that is released along with the energy stored in the leaf spring to propel the wearer forward. A ribbon clutch prevents the foot member from rotating in one direction beyond a predetermined limit position. A controllable damper is employed to lock the ankle joint or to absorb mechanical energy as needed. The controller and sensing mechanisms control both the actuator motor and the controllable damper at different times during the walking cycle for level walking, stair ascent, and stair descent.