Mechanical Prosthetic Knee Locking for Safe Stair Descent
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Solution Overview
Problem
Existing mechanical knee prostheses for femoral amputees face challenges in maintaining stability and reliability, particularly during tasks like descending stairs, due to involuntary mode switching and lack of shock-absorbing systems, leading to potential falls.
Innovation Solution
A fully mechanical locking system with an articulated linkage device and adjustable pendulum mechanism that ensures safe switching between weight-bearing and oscillating modes only when the prosthesis is in a hyperextended position and slightly inclined forward, using a piston with a modified pendulum and adjustable offset center of gravity to prevent premature mode changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hyperextension control mechanism is used to enable swing phase activation, then leg flexion is easier during push-off phase, but the prosthesis risks involuntary unlocking during extension which could cause falls
Solution Approach 1:
The locking system is designed to require a specific preliminary condition (hyperextended position with forward inclination) before mode switching can occur. The articulated linkage device must first achieve the precise geometric configuration defined by the predetermined angles, ensuring that mode transition is prepared only when the prosthesis is in the correct position, thus preventing premature or involuntary unlocking
Solution Approach 2:
The system incorporates geometric feedback through the articulated linkage device that continuously monitors the relative positions of the femoral and tibial components. The locking system responds to the geometric configuration feedback by enabling or disabling mode switching based on whether the predetermined angular conditions are met, creating a closed-loop control mechanism that enhances reliability
2Ease of operation
If electronic control systems with sensors are used to simulate healthy knee joint, then leg movement naturalness is improved, but manufacturing cost and energy consumption increase significantly
Solution Approach 1:
The patent replaces electronic control systems, sensors, and processors with a purely mechanical articulated linkage device. The complex electronic algorithms for determining knee flexion are substituted by mechanical geometric relationships between linkage components that automatically enforce the desired movement patterns through their physical configuration, eliminating the need for expensive electronics while maintaining natural motion
Solution Approach 2:
The articulated linkage device is designed to automatically regulate knee joint behavior without external control systems. The mechanical structure itself performs the function of sensing and controlling leg movement based on its geometric configuration, making the system self-regulating and eliminating dependencies on powered electronic components
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
Enhances reliability and stability by ensuring safe and conditional mode transitions, minimizing manufacturing costs and labor, and maintaining ergonomic design without requiring significant structural modifications.
Implementation Method 1
a piston, preferably hydraulic, simulating the muscle group associated with them
Implementation Method 2
an articulated linkage device (2) comprising a locking system (3), arranged to allow the activation of the second mode of operation
Implementation Method 3
a piston with a modified pendulum and adjustable offset center of gravity
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A hinged connecting device (2) for a prosthesis (1) for a femoral amputee, connecting the femoral part (101) and the tibial part (102) of same in a hinged manner, and moreover comprising a damping mechanism (20) intended to counter a predetermined resistance at least during bending of the prosthesis (1), by replacing the muscle groups usually used for this purpose. The damping mechanism (200) is capable of being switched between a first operating mode (M1), selected by default, in which the value of the resistance corresponds to a first maximum value (Vmax), and a second operating mode (M2), that can be actuated only in a hyperextension position (P0) of the prosthesis (1), in which the resistance value corresponds to a second minimum value (Vmin); and the hinged connecting device (2) moreover comprises a fully mechanical locking system (3), arranged in order to allow the second operating mode (M2) to be activated only when the inclination of the tibial part (102) exceeds a first predetermined oriented angle (X1) relative to the vertical.