Prosthetic Ground Contact Sensor Arrays With Compliant Displacement Sensing
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Solution Overview
Problem
Existing lower-limb prosthetic and orthotic devices face challenges with high costs, complex integration requirements, and inadequate handling of asymmetrical acceleration spikes during gait transitions, leading to reduced performance and reliance on advanced signal processing.
Innovation Solution
A ground contact sensor array with a selectively compliant mechanical structure and non-contact displacement sensors, such as Hall effect sensors, is used to detect changes in distance between moving and non-moving parts of the prosthetic device, allowing for robust control signals based on load detection and minimizing sensitivity to torque loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-contact displacement sensors are used to detect ground contact, then measurement precision is improved, but device complexity increases due to the need for selectively compliant mechanical structures and sensor arrays
Solution Approach 1:
The prosthetic device is divided into moving and non-moving portions with multiple sensors distributed across the structure. This segmentation allows each sensor to independently measure local displacements, improving overall measurement precision while distributing the complexity across modular components rather than a single complex mechanism
Solution Approach 2:
The selectively compliant mechanical structure changes its stiffness parameters dynamically - being compliant in certain directions to allow movement and rigid in other directions to provide stable sensor mounting. This parameter change enables the structure to simultaneously support precise measurement and manage mechanical complexity
2Manufacturing precision
If the sensor array is mounted on a rigid structure, then manufacturing precision is improved, but reliability decreases due to sensitivity to torque loads and inertial effects
Solution Approach 1:
Different portions of the mechanical structure have different mechanical properties - some areas are designed to be rigid for stable sensor mounting, while other areas are compliant to isolate sensors from torque loads and inertial effects. This local differentiation allows the system to simultaneously achieve manufacturing precision and measurement reliability
Solution Approach 2:
The selectively compliant mechanical structure acts as an intermediary between the rigid prosthetic components and the sensors. It transmits only the relevant displacement information to the sensors while filtering out unwanted torque loads and inertial effects, thereby protecting measurement reliability
3Measurement precision
If multiple sensors are used to detect ground contact, then measurement precision is improved, but device complexity increases due to integration requirements
Solution Approach 1:
The array of non-contact displacement sensors serves multiple functions: detecting ground contact, measuring load magnitude, determining gait phase, and providing redundancy. This multi-functionality justifies the increased number of sensors while managing overall system complexity through unified sensor technology and processing approach
4Reliability
If the prosthetic device uses a compliant mechanical structure, then reliability is improved by reducing sensitivity to torque loads, but manufacturing precision becomes more difficult
Solution Approach 1:
The mechanical structure uses controlled changes in stiffness parameters through selectively compliant design. By adjusting the compliance parameters in specific regions, the structure achieves reliability (insensitivity to torque loads) while maintaining manufacturability through standardized compliant mechanism designs that can be fabricated with conventional tolerances
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 sensor array provides accurate and repeatable load measurements, reduces sensitivity to inertial loading, and maintains sensitivity around zero-load points, enabling effective stance and swing phase control with reduced installation precision requirements and improved robustness against sensor failure.
Implementation Method 1
non-contact displacement sensors, such as Hall effect sensors, is used to detect changes in distance between moving and non-moving parts of the prosthetic device
Data Source
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AI summary
Systems, devices and methods for detecting ground contact with a lower-limb POD. A sensor array for the POD on a first or second body may include two or more sensors in an array that each detect a distance to a respective target on the other of the first or second body. The first and second bodies may move relative to each other thereby changing an offset distance or distances between the two bodies which is detected by the sensors. In some embodiments, the sensors may include Hall Effect sensors that detect distances to respective magnets. Load data based on the detected distances may be generated for control of the POD, such as for stance phase control.