Bicycle Crankarm Stress Detector Positioning for Torque Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bicycle crankarms with stress/strain detectors for power or torque meters do not accurately detect pedaling power or torque, especially when the detector is positioned close to the bottom bracket spindle.
Innovation Solution
A bicycle crankarm with a stress/strain detector oriented along the length direction, fixed at a distance from the rotation axis such that the ratio of this distance to the crankarm length is between 0.45 and 0.65, maximizing the sensitivity ratio for detecting pedaling power or torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the stress/strain detector is positioned close to the bottom bracket spindle to maximize sensitivity, then the detection sensitivity increases, but the accuracy of pedaling power or torque detection deteriorates due to secondary stresses from the opposing crankarm
Solution Approach 1:
The patent applies local quality by positioning the stress/strain detector at a specific location along the crankarm (at a distance of 0.45-0.65 times the crankarm length from the rotation axis) rather than uniformly throughout. This localized positioning optimizes the balance between detection sensitivity and accuracy by placing the detector in a region where it can sense pedaling forces effectively while minimizing interference from secondary stresses transmitted through the bottom bracket spindle from the opposing crankarm.
2Measurement precision
If the detector is positioned at a specific distance ratio (0.45-0.65) from the rotation axis, then the sensitivity ratio for detecting pedaling power is maximized, but the device complexity increases due to precise positioning requirements
Solution Approach 1:
The patent applies parameter changes by defining a specific range for the distance ratio (0.45-0.65) rather than a single fixed value. This approach allows manufacturing flexibility while maintaining optimal performance, as any position within this range provides acceptable sensitivity ratio. The parameter optimization balances measurement precision with ease of manufacturing and assembly.
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
This configuration allows for a more accurate detection of pedaling power or torque, minimizing the impact of secondary stresses from the opposing crankarm and improving the reliability of readings, especially in composite material crankarms.
Implementation Method 1
the strain gage that is in top position is subjected to and detects a dilation or elongation, while the strain gage that is in bottom position detects a contraction or compression when the cyclist applies a force on the pedal
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A bicycle crankarm (22) for mounting on the bicycle transmission side, comprising a main body (38) having a length (Lp) measured along a length direction (L) from a rotation axis (X) to a pedal axis (Y1) of the crankarm (22), said crankarm (22) comprising at least one stress/strain detector (100) for a torque meter or a power meter, oriented along the length direction (L), characterized in that said at least one detector is fixed at a distance (Do), measured from the center (C) of said at least one stress/strain detector (100) to the rotation axis (X) of the crankarm (22), such that the ratio between said distance (Do) and said length (Lp) is comprised in the range 0.45-0.65.