Minimum Jerk Swing Control for Powered Prostheses
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Solution Overview
Problem
Powered prostheses for individuals with transfemoral amputations face challenges in achieving biologically accurate swing movement due to impedance-inspired control methods, which do not allow direct regulation of swing duration, leading to asymmetric gait patterns and difficulties in adapting to variable cadence and walking speed.
Innovation Solution
A control approach using minimum jerk trajectory polynomials to directly control swing duration, independent of joint angle and velocity at the stance-to-swing phase transition, allowing for natural gait symmetry and proper foot clearance across different walking conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If impedance-inspired control is used to control joint torque as a function of angle and velocity, then the prosthesis can provide biologically plausible swing movement, but swing duration cannot be directly regulated and depends on dynamic interaction with user and environment
Solution Approach 1:
The patent applies preliminary action by pre-defining the swing phase duration as a controlled parameter before the swing movement occurs. The controller calculates the desired swing phase duration based on stance phase duration and walking speed, then uses this predetermined timing information to generate the swing trajectory, rather than allowing swing duration to emerge from dynamic interactions during the movement.
Solution Approach 2:
The patent implements dynamics by making the swing phase duration adaptive to walking conditions. The controller dynamically adjusts swing duration based on real-time measurements of stance phase duration and walking speed, allowing the prosthesis to automatically adapt to varying gait conditions while maintaining direct control over the swing timing.
2Manufacturing precision
If impedance parameters are regulated to modify swing trajectory, then swing path can be optimized, but swing duration remains undefined a priori and cannot be controlled independently
Solution Approach 1:
The patent applies preliminary action by pre-calculating the desired swing phase duration based on stance phase duration and walking speed before generating the swing trajectory. This predetermined duration is then used to constrain the swing movement, ensuring that swing duration is controlled independently of trajectory shaping through impedance parameter regulation.
Solution Approach 2:
The patent implements segmentation by separating the control of swing trajectory from the control of swing duration. The swing phase is divided into two independent control dimensions: (1) trajectory control through impedance parameters (stiffness, damping, equilibrium values), and (2) duration control through direct timing regulation based on stance phase duration and walking speed. This allows independent optimization of both trajectory and timing.
3Ease of operation
If user pulls thigh forward to initiate swing movement, then swing can be initiated, but asymmetric gait pattern is produced and natural walking is compromised
Solution Approach 1:
The patent applies self-service by enabling the prosthesis to automatically initiate and control swing movement without requiring active user pulling actions. The controller uses sensory feedback (position, velocity, acceleration sensors) to detect stance-to-swing transition and automatically generates the appropriate swing trajectory, allowing the prosthesis to serve itself rather than requiring continuous user input for swing initiation.
Solution Approach 2:
The patent implements feedback by using sensory inputs from position, velocity, and acceleration sensors to continuously monitor the gait cycle and adjust swing initiation timing accordingly. The controller detects the stance-to-swing transition through feedback signals and automatically initiates swing movement at the appropriate moment, eliminating the need for user pulling actions and restoring natural gait symmetry.
Data Source
AI summary
We present a novel swing phase control module for powered transfemoral prostheses based on minimum jerk theory. The control module allows physiologically appropriate swing movement at any walking speed, regardless of the stance controller action. Preliminary validation in a transfemoral amputee subject demonstrates that the control module provides physiological swing timing, without speed or patient-specific tuning.