Powered Prosthesis Stair Descent Control via Finite State Model
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Solution Overview
Problem
Existing powered lower limb prostheses are unable to provide biomechanically healthy stair ascent and descent due to the inability to deliver net positive power at the knee and ankle joints during stair ascent and inappropriate ankle configuration during forefoot strike in stair descent.
Innovation Solution
A method and system for controlling powered knee and ankle prostheses using a finite state model that transitions between states based on real-time sensor information, including powered knee extension and ankle push-off for stair ascent, and powered plantarflexion and resistive dorsiflexion for stair descent, to emulate healthy gait patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an energetically passive prosthesis is used, then the device is simpler and does not require power sources, but it is fundamentally unable to provide net positive power at the knee and ankle joints during stair ascent
Solution Approach 1:
The prosthesis employs dynamically adjustable damping elements that can modulate their resistance characteristics in real-time based on the gait phase and loading conditions. This allows the passive structure to adapt its mechanical properties to provide appropriate power assistance during stair ascent without requiring active power sources or complex control systems.
Solution Approach 2:
The damping coefficients of the prosthetic joints are varied as a function of joint angle, angular velocity, and loading conditions. By changing these parameters dynamically, the passive prosthesis can optimize its power delivery characteristics for different activities including stair ascent, where net positive power is required at the knee and ankle joints.
2Ease of operation
If existing passive ankle/foot prostheses are used, then the structure is simpler, but they are unable to provide appropriate ankle posture during terminal swing phase to set up forefoot strike and unable to absorb energy during the loading phase of stair descent
Solution Approach 1:
The ankle prosthesis incorporates dynamically adjustable damping elements that modify their resistance characteristics based on the gait phase. During terminal swing, the damping is adjusted to facilitate forefoot strike by allowing appropriate ankle dorsiflexion. During the loading phase of stair descent, the damping is increased to absorb impact energy, providing reliable shock attenuation.
Solution Approach 2:
The prosthetic system uses real-time feedback from load cells and angle sensors to adjust damping characteristics. The load cell detects ground reaction forces and ankle moment, while angle sensors monitor joint position, allowing the damping elements to respond dynamically to loading conditions and maintain appropriate ankle posture for forefoot strike.
3Adaptability or versatility
If microprocessor control with modulated damping elements is integrated, then the capability to accommodate variation in gait speed is enhanced, but the capabilities remain inferior relative to a healthy joint during stair ascent and descent
Solution Approach 1:
The damping elements are designed with nonlinear characteristics that provide different resistance profiles for different gait phases and loading conditions. This dynamic behavior, combined with microprocessor control, enables the prosthesis to accommodate variations in gait speed while also providing superior performance during stair ascent and descent by optimizing power delivery and energy absorption.
Solution Approach 2:
The damping coefficients are varied as a function of multiple parameters including joint angle, angular velocity, and ground reaction forces. This multi-parameter control strategy allows the prosthesis to adapt to different gait speeds while maintaining reliable performance during challenging activities like stair ascent and descent, overcoming the limitations of earlier single-parameter control systems.
Data Source
AI summary
Systems and methods of operating a lower limb device having at least a powered joint are provided. A method includes configuring the device to a first state in a finite state model for a current activity mode including a stair ascent mode or a stair descent mode. The method also includes, based on real-time sensor information, transitioning the device between different states in the finite state model when pre-defined criteria for transitioning among the different states are met. In the method, the finite state model for stair ascent includes lifting and swing phases, where the lifting phase includes a powered knee extension and a powered ankle push-off. The finite state model for stair descent includes yielding and swing states, where the swing states include providing a powered plantarflexion of the powered ankle joint and the yielding states include providing a resistive and passive plantarflexion of the powered ankle joint.