Powered Ankle Prosthesis Impedance Control
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Solution Overview
Problem
Transtibial amputees using passive dynamic-elastic-response foot/ankle prostheses experience limited biomechanical behavior emulation, as these devices only provide a small subset of the varied stiffness and damping behaviors of a healthy ankle, failing to replicate powered push-off and controlled motion across different activities and terrains.
Innovation Solution
A powered ankle prosthesis with a sensing, actuation, and transmission system capable of emulating the range of healthy ankle joint impedances, utilizing a control methodology based on software-driven impedance emulation, including a finite-state-machine structure with virtual spring and damper systems, and sensors for real-time feedback to generate and dissipate biomechanical levels of power and torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive dynamic-elastic-response foot/ankle prostheses are used, then the device structure is simple, but the biomechanical behavior emulation is limited
Solution Approach 1:
The patent applies dynamics by transitioning from a static passive spring structure to a dynamic controlled system. The ankle prosthesis uses active actuators and control systems that continuously adjust stiffness, damping, and equilibrium point based on real-time sensing of user intent and gait phase, enabling the device to adapt its mechanical behavior dynamically throughout the gait cycle and across different activities.
Solution Approach 2:
The patent replaces the purely mechanical passive spring system with a mechatronic system that integrates sensors, processors, and active actuators. This substitution enables sophisticated control strategies including impedance control, torque control, and position control, allowing the prosthesis to emulate the full range of healthy ankle behaviors that cannot be achieved with passive mechanical elements alone.
2Ease of operation
If passive ankle prostheses are used, then the device is simple to operate, but it cannot provide powered push-off or controlled motion generation
Solution Approach 1:
The patent implements self-service through autonomous control systems that automatically sense user intent, determine gait phase, and generate appropriate torque commands without requiring manual input from the user. The system uses sensors to detect foot contact, shank angle, and other biomechanical parameters, then autonomously adjusts ankle moment and stiffness to provide powered push-off, controlled motion generation, and adaptive behavior across different terrains and activities.
3Adaptability or versatility
If a powered ankle prosthesis with full biomechanical emulation is implemented, then the biomechanical behavior range is comprehensive, but the control system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the control system into distinct functional modules: sensing subsystems for detecting user intent and gait parameters, processing subsystems for determining gait phase and computing control commands, and actuation subsystems for generating ankle torque. The gait cycle is also segmented into discrete phases (swing, stance, push-off) with specific control strategies for each, allowing complex biomechanical emulation to be achieved through coordinated simple modular components.
4Measurement precision
If software-driven impedance emulation is used, then the healthy ankle behavior emulation is accurate, but the computational requirements increase
Solution Approach 1:
The patent implements parameter changes by dynamically adjusting impedance parameters (stiffness, damping, equilibrium point) based on gait phase, user intent, and terrain conditions. The control system computes time-varying torque commands that modify the effective mechanical impedance of the ankle prosthesis throughout the gait cycle, enabling accurate emulation of healthy ankle behavior where impedance varies continuously during movement rather than remaining fixed.
Data Source
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AI summary
Described herein are systems and methods for a powered ankle/foot prosthesis and controller that utilizes piecewise emulated passive impedances to provide for walking at various cadences and on various slopes and for ground slope adaptive standing. A powered prosthesis using these systems and methods is capable of emulating any physical behavior provided by the healthy joint, and additionally describes a control system that utilizes the sensing and actuation system on the prosthesis to provide appropriate ankle joint impedances. Further, the control system incorporates a finite-state-based structure, and within each state, emulates the behavior of the healthy joint with strictly passive impedance functions.