Crank Arm Cavity Embedded Strain Sensor
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Solution Overview
Problem
Conventional strain gauges attached to carbon-fiber crank apparatuses face challenges in accurately measuring pedaling torque due to difficulty in direct attachment and non-linear strain characteristics, leading to distorted data and reduced accuracy, which requires inconvenient calibration processes.
Innovation Solution
A crank apparatus with a thin material layer having uniform strain characteristics embedded in a cavity of the crank arm, allowing a sensing element to measure the force applied to the crank arm, thereby improving measurement accuracy and eliminating the need for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a strain gauge is directly attached to the carbon-fiber crank surface using a clear coat, then the strain gauge can be mounted on the carbon-fiber material, but the deformation of the carbon-fiber material transmitted to the clear coat causes distorted measurement data
Solution Approach 1:
The patent introduces a thin layer of material with uniform strain characteristics as an intermediary between the carbon-fiber crank and the strain gauge. This intermediate layer transforms the non-uniform strain from the carbon-fiber material into uniform strain that the strain gauge can measure accurately, resolving the contradiction between ease of attachment and measurement precision.
Solution Approach 2:
The patent changes the strain characteristic parameter from non-uniform (carbon-fiber) to uniform (intermediate material) to enable accurate measurement. By selecting a material with uniform strain characteristics, the system transforms the problematic non-linear strain distribution into a measurable uniform strain field.
2Strength
If the crank is manufactured of carbon-fiber material with different stacking layer directions, then the crank achieves desired structural properties, but the torsion and deformation become uniformed causing non-linear strain characteristic change
Solution Approach 1:
The thin layer of material serves as a mediator that decouples the structural requirements of the carbon-fiber crank from the measurement requirements of the strain gauge. It accepts the non-uniform deformation from the carbon-fiber structure and converts it into uniform strain for accurate measurement.
Solution Approach 2:
The patent applies homogeneity by selecting an intermediate material with uniform strain characteristics that distributes the deformation evenly across its structure. This homogeneous material property ensures linear strain change that the strain gauge can measure accurately, regardless of the anisotropic carbon-fiber structure underneath.
3Measurement precision
If a specific calibrating process is performed to increase measuring accuracy, then measurement precision improves, but user convenience decreases due to the calibration requirement
Solution Approach 1:
The uniform strain characteristic material essentially performs the calibration function automatically through its inherent uniform deformation properties. The system becomes self-calibrating in a sense, as the material's uniform strain distribution naturally provides linear measurement output without requiring external calibration procedures by the user.
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 the accuracy of pedaling force measurement by ensuring uniform strain deformation and direct force transmission, providing a more convenient user experience by eliminating the need for calibration.
Implementation Method 1
The thin material layer is adapted to be deformed corresponding to the deformation of the crank arm. The at least one sensing element is adapted to measure the corresponding strain of the thin material layer
Data Source
AI summary
A crank apparatus includes a crank arm having at least one cavity on one of the surfaces of the crank arm, at least one thin material layer embedded within the at least one cavity and having an exposed outer surface, and at least one sensing element attached to the outer surface of the thin material layer. The crank arm is manufactured of a material with non-uniform strain characteristics, the thin material layer is manufactured of a material with uniform strain characteristics, the crank arm is adapted to be deformed by a force, the thin material layer is adapted to be deformed correspondingly with the deformation of the crank arm, the at least one sensing element is adapted to measure the corresponding strain of the thin material layer to measure the force applied on the crank arm. A bicycle and a stationary exercise bicycle equipped with the crank apparatus are further provided.