Capacitive Force Sensor Decoupling Normal and Shear Measurements
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Solution Overview
Problem
Existing force sensors struggle to effectively decouple normal and shear force measurements, particularly in applications like climbing robots where reliable grip sensing is crucial, and existing solutions are either impractical for small robots or lack sensitivity to shear loads.
Innovation Solution
A capacitive force sensor design featuring a dielectric layer of non-conductive elastomer that is incompressible in the normal direction but deflects in the shear direction, combined with parallel conductive and shear channel traces, allowing for high sensitivity in shear force measurements while rejecting normal forces, enabling robust and lightweight force sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional force sensor is used to measure both normal and shear forces, then the sensor can detect force magnitudes, but the normal and shear force measurements are coupled and cannot be independently measured
Solution Approach 1:
The sensor is divided into separate functional layers: a first capacitive structure for normal force measurement and a second capacitive structure for shear force measurement. This segmentation allows independent measurement of normal and shear forces without coupling, resolving the measurement precision issue while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
The patent introduces a layered structural dimension with conductive plates arranged in specific orientations. The first capacitive structure uses plates oriented for normal force sensitivity, while the second uses plates oriented for shear force sensitivity. This dimensional arrangement in the capacitive structure enables decoupled measurement along different force directions.
2Measurement precision
If an optical sensor with high spatial resolution is used to measure pressure distributions, then measurement precision is improved, but the device becomes impractical for packaging into small robots and is not lightweight
Solution Approach 1:
The patent replaces complex optical measurement systems with a capacitive sensing mechanism. The capacitive structures detect force through electrical field changes rather than optical paths, eliminating the need for heavy optical components while maintaining measurement precision. This substitution achieves lightweight design suitable for small robots.
Solution Approach 2:
The patent changes the measurement parameter from optical properties (light reflection, refraction) to electrical properties (capacitance). By measuring capacitance changes in the capacitive structures under applied force, the system achieves accurate force measurement without the weight penalty of optical components, enabling integration into lightweight robotic systems.
3Measurement precision
If a sensor measures both normal and shear forces with the same structure, then the device complexity is reduced, but the sensitivity to shear loads is insufficient
Solution Approach 1:
The patent applies local quality by designing the second capacitive structure specifically with high sensitivity to shear loads. The conductive plates in the second structure are oriented and positioned to maximize shear force detection capability. This localized optimization of the capacitive structure provides enhanced shear sensitivity without requiring complete redesign of the entire sensor system.
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 achieves high sensitivity in both normal and shear force directions, providing a robust and cost-effective solution for force and torque sensing, suitable for applications in robotics and prosthetics, with improved durability and reduced hysteresis compared to existing technologies.
Implementation Method 1
parallel conductive traces and the parallel shear channel traces provide capacitive shear force measurement sensitivity
Implementation Method 2
the dielectric layer is incompressible in the a normal direction and deflects in a shear direction
Implementation Method 3
the dielectric layer is a non-conductive elastomer that is incompressible in the a normal direction
Data Source
AI summary
A capacitive force sensor is provided that includes a first support layer and a second support layer, a dielectric layer disposed between the first support layer and the second support layer, where the dielectric layer is a non-conductive elastomer that is incompressible in the a normal direction and deflects in a shear direction, a layer of parallel conductive traces disposed between and bonded to the dielectric layer and the first support layer, and a conductive layer of parallel shear channel traces having at least two distinct channels disposed between and bonded to the dielectric layer and the second support layer, where the parallel conductive traces and the parallel shear channel traces are locally parallel to each other and provide capacitive shear force measurement sensitivity while rejecting normal forces, where the normal force measurement is decoupled from the shear force measurement.