Prosthetic Knee Rotary Angle Sensing for Gait Resistance Control
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Solution Overview
Problem
Existing microprocessor-controlled prosthetic knees face challenges in accurately measuring knee joint angles due to reliance on indirect methods that require additional components, are prone to mechanical failures, or have limited accuracy, leading to potential malfunction and reduced functionality.
Innovation Solution
A prosthetic knee system utilizing a diametrically polarized magnet and a magnetic rotary position sensor, combined with an inertial measurement unit (IMU) and a control algorithm, to directly measure knee joint angles and adjust flexion and extension resistance based on gait phases without requiring user-specific information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a hall effect sensor measures magnet displacement along a horizontal track to determine knee joint angle, then the knee joint angle can be detected, but the system requires additional componentry, has more moving parts, and is prone to mechanical failures
Solution Approach 1:
The patent extracts the magnet from its traditional linear track and repositions it directly on the rotating axial pin. This removes the horizontal track component entirely, eliminating the linear sliding mechanism while preserving the angle detection capability through direct rotational measurement.
Solution Approach 2:
Instead of measuring linear magnet displacement along a fixed track (traditional approach), the patent inverts the approach by attaching the magnet to the rotating pin itself and measuring its rotational position directly. This transforms a linear measurement problem into a rotational measurement problem, simplifying the mechanism.
2Use of energy by moving object
If an induction sensor is used to detect knee joint angle by measuring metal material thickness, then the power requirements are reduced, but the measurement accuracy decreases
Solution Approach 1:
The patent replaces the induction sensor (electromagnetic field-based) with a Hall effect sensor that directly detects magnetic field strength from a diametrically polarized magnet. This substitution maintains low power requirements while significantly improving measurement accuracy through direct magnetic field sensing.
Solution Approach 2:
The patent changes the sensing parameter from measuring metal thickness (induction sensor) to measuring magnetic field strength (Hall effect sensor). This parameter change enables more precise angle detection while maintaining energy efficiency, as the Hall effect sensor responds directly to the magnet's position without requiring complex electromagnetic induction measurements.
3Measurement precision
If a linear Hall Effect sensor detects magnetic field presence to measure knee angle, then the system can detect gait phases, but the sensor is limited to measuring only linear motion
Solution Approach 1:
The patent changes from using a linear Hall effect sensor to a rotary Hall effect sensor that can detect rotational position. This parameter change enables the sensor to measure the rotational angle of the knee joint directly, providing both accurate gait phase detection and the versatility to handle rotational motion.
Solution Approach 2:
Instead of using a linear sensor to indirectly infer rotational position, the patent inverts the approach by using a rotary-capable Hall effect sensor that directly measures rotational angle. This provides both the precision needed for gait detection and the versatility for rotational measurement.
4Measurement precision
If multiple sensors and user-specific information are used to control prosthetic knee resistance, then the resistance control accuracy is improved, but the system complexity and weight increase
Solution Approach 1:
The patent makes the knee angle sensor the central multi-functional element that provides all necessary information for resistance control. By accurately measuring the knee joint angle throughout the gait cycle, this single sensor replaces multiple sensors and eliminates the need for user-specific data input, achieving both simplicity and control accuracy.
Solution Approach 2:
The system uses the knee angle measurement itself to automatically determine gait phase and adjust resistance without requiring external user-specific information. The angle data serves multiple purposes: detecting gait phase, determining resistance level, and controlling the prosthetic knee autonomously, eliminating the need for additional sensors or user input.
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 system provides accurate and reliable resistance control, reduces complexity and weight, enhances battery life, and improves functionality by eliminating the need for additional sensors and user-specific data, ensuring smooth gait transitions and enhanced stability.
Implementation Method 1
a diametrically polarized magnet is located on the axial pin and a linear Hall Effect sensor is positioned in front of the upper bone segment. As the knee joint moves, the Hall Effect sensor detects the magnetic field presence.
Implementation Method 2
A hall effect sensor may be positioned on a circuit board at the front of the upper bone segment which measures the displacement of the magnet along the horizontal track.
Data Source
AI summary
A prosthetic knee uses a hydraulic damper to regulate the rotation of the prosthetic knee joint. An IMU sensor detects the direction of rotation, tilt, and/or speed of the prosthetic knee. A magnetic rotary on-axis position sensor located at the joint between the upper and lower portions of the prosthetic knee measures the motion of the upper portion of the knee by detecting the magnetic field which is generated by a diametrically polarized magnet. A microprocessor correlates the measured motion to a knee joint angle. The microprocessor detects a user's stage of gait based on the measurements of the IMU sensor and on-axis position sensor and adjusts the resistance provided by the hydraulic damper according to a corresponding stage of gait.