Laterally Offset FSR Layers for Shear Force and Torque Measurement
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Solution Overview
Problem
Current force sensors struggle to accurately measure shear force and vertical torque outside controlled laboratory settings, particularly in wearable devices like footwear, due to sensitivity to environmental changes and the lack of sensors for measuring these forces in real-world applications.
Innovation Solution
The development of force sensors with laterally offset force-sensitive resistor layers that move in response to shear force and torque, integrated into wearable devices such as insoles, allowing for real-time measurement of shear forces and torques using force-sensing resistors (FSRs) configured in interdigitated patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional force sensors are used in wearable devices, then they can measure normal forces, but they cannot accurately measure shear forces and vertical torques in real-world applications
Solution Approach 1:
The sensor is divided into multiple independent FSR elements arranged in specific patterns (interdigitated or laterally offset). Each FSR element measures force in a specific direction, and by combining readings from multiple elements, the system can accurately calculate shear forces and torques. This segmentation allows the sensor to measure multiple force components simultaneously while maintaining wearability.
Solution Approach 2:
Different regions of the sensor have different FSR element configurations optimized for measuring specific force components. The interdigitated or laterally offset patterns create local sensitivity zones that respond preferentially to shear forces or torques in particular directions, enabling accurate measurement of these forces while the overall sensor remains thin and wearable.
2Measurement precision
If laterally offset FSR layers are used to measure shear force and torque, then measurement capability is improved, but sensor structure becomes more complex
Solution Approach 1:
Multiple FSR layers are combined in a single sensor assembly with laterally offset arrangements. The upper and lower FSR layers are positioned at different lateral locations, and their combined responses enable calculation of both shear forces and torques. This merging approach achieves enhanced measurement capability while keeping the overall structure integrated and manageable.
Solution Approach 2:
The sensor transitions from a single-plane configuration to a multi-layer three-dimensional structure with lateral offsets. By adding the vertical dimension (multiple layers) and lateral positioning, the sensor can distinguish between different force components (shear vs. torque) that would be indistinguishable in a single-plane configuration, thereby improving measurement precision without excessive complexity.
3Measurement precision
If interdigitated FSR patterns are implemented, then shear force and torque measurement is enabled, but manufacturing precision requirements increase
Solution Approach 1:
The FSR layers are deliberately positioned with asymmetric lateral offsets rather than perfect alignment. The upper and lower layers are offset by specific distances that create the interdigitated pattern. This asymmetric design is intentionally built into the manufacturing process, and as long as the offset distances are consistent, the exact absolute positions are less critical, thereby reducing manufacturing precision requirements while maintaining measurement accuracy.
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
Enables accurate and real-time measurement of shear forces and torques in wearable devices, enhancing athletic performance monitoring and injury prediction, while being cost-effective and minimally intrusive.
Implementation Method 1
an upper force-sensitive resistor layer applied to the upper conductive layer; and a lower force-sensitive resistor layer applied to the lower conductive layer wherein the lower force-sensitive resistor layer and the upper force-sensitive resistor layer are laterally offset under a zero-shear force condition and/or a zero-torque condition and are moveable laterally towards or away from each other in response to a shear force and/or a torque
Data Source
AI summary
A force sensor and sensor system for measuring shear force and/or vertical torque. The force sensor has an upper substrate layer, a lower substrate layer, an upper sensor portion, and a lower sensor portion. The upper sensor portion has an upper conductive layer and an upper force-sensitive resistor layer applied to the upper conductive layer. The lower sensor portion has a lower conductive layer applied to the upper surface of the lower substrate layer and a lower force-sensitive resistor layer applied to the lower conductive layer. The lower force-sensitive resistor layer and the upper force-sensitive resistor layer are laterally offset under a zero-shear force condition and/or a zero-torque condition and the lower force-sensitive resistor layer and the upper force-sensitive resistor layer are moveable laterally towards or away from each other in response to a shear force and/or a torque.