Prosthetic Knee Impedance Control for Amputee Mobility
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Solution Overview
Problem
Above knee amputees using commercially available trans-femoral prostheses experience discomfort due to mismatched rotation axes between the prosthesis and the motion assisting apparatus, leading to limited mobility and discomfort during activities like stair climbing, as existing solutions do not adequately account for the weight and kinetic parameters of the assisting apparatus.
Innovation Solution
A wearable artificial leg motion assisting apparatus with a drive unit, biological signal detection, and impedance adjustment, which includes sensors for detecting biological signals, kinetic parameters, and ground reaction forces to adjust mechanical impedance and control the drive unit, ensuring smooth power transmission to the knee joint without discomfort, even if the axes do not match.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a wearable-type motion assisting apparatus is attached to a commercially-available trans-femoral prosthesis, then active knee joint movement is enabled, but the mismatched rotation axes cause discomfort to the wearer
Solution Approach 1:
The system dynamically changes the mechanical impedance parameters of the motion assisting apparatus to match the kinetic parameters of the wearer's gait. By estimating parameters such as moment of inertia, viscous friction coefficient, and Coulomb friction coefficient during calibration and adjusting them in real-time, the system optimizes power transmission efficiency and reduces discomfort caused by axis mismatch between the prosthesis and actuator.
2Productivity
If the motion assisting apparatus is mounted on the trans-femoral prosthesis, then stair climbing ability is improved, but the weight of the apparatus adds to the burden on the wearer
Solution Approach 1:
The system applies partial active assistance rather than full active control. The motion assisting apparatus provides targeted torque support during specific phases of the gait cycle, particularly during stair climbing, while relying on the passive mechanical properties of the prosthesis and the wearer's own muscle strength for other movements. This reduces the overall weight requirement while maintaining functionality for demanding tasks.
3Reliability
If impedance adjustment is performed based on kinetic parameters, then power transmission efficiency is improved, but the complexity of the control system increases
Solution Approach 1:
The system performs preliminary calibration to estimate the kinetic parameters of the specific trans-femoral prosthesis before normal operation. During this calibration phase, the system measures physical quantities and calculates parameters such as moment of inertia and friction coefficients. These pre-estimated parameters are then used to configure the impedance control, simplifying real-time operation while maintaining high power transmission efficiency.
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 apparatus allows for comfortable and natural movement, including stair climbing, by accurately adjusting mechanical impedance and controlling the drive unit based on detected biological signals and kinetic parameters, reducing discomfort and enhancing mobility for above knee amputees.
Implementation Method 1
a biological signal detection unit that detects an electrical potential as a biological signal generated in association with a thigh motion of the wearer
Implementation Method 2
a drive unit that is coupled to the thigh frame and the lower leg frame and drives actively or passively in conjunction with a thigh motion of the wearer
Implementation Method 3
an impedance adjustment unit that adjusts mechanical impedance specific to the knee joint coupling on the basis of the kinetic parameter estimated by the parameter estimation unit
Data Source
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AI summary
An artificial leg motion assisting apparatus and an artificial leg motion assisting method which are capable of transmitting knee joint motive power to a commercially-available trans-femoral prosthesis without making a wearer feel a sense of discomfort. When the artificial leg motion assisting apparatus is attached to the commercially-available trans-femoral prosthesis, a control unit controls a drive unit by a specified control method on the basis of mechanical impedance adjusted by an impedance adjustment unit and transmits output of the drive unit to a knee joint coupling.