Torque Sensor Spindle Strain Gauge Shear Pattern
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Solution Overview
Problem
Current power meters for human-propelled vehicles face challenges in accurately measuring power due to the complexity of decoupling bending and torsion strains, which is costly and often requires expensive calibration, especially for pedal-based approaches.
Innovation Solution
A torque sensor with a spindle and pair of strain gauge grids mounted in a shear pattern, electrically connected in a Wheatstone Bridge arrangement to measure shear strain from torsional forces while negating shear strain from bending forces, allowing for direct and accurate power measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauges are mounted to measure both bending and torsion strains simultaneously, then comprehensive strain measurement is achieved, but decoupling these strains becomes complicated and costly
Solution Approach 1:
The patent applies local quality by mounting strain gauges at specific orientations (0 degrees, 45 degrees, and 90 degrees) relative to the crank arm axis. Each gauge measures a specific combination of bending and torsional strains, allowing mathematical decoupling to isolate pure torsional strain. This targeted placement transforms a complex measurement problem into a solvable system of equations.
Solution Approach 2:
The patent replaces complex mechanical strain decoupling mechanisms with an electrical/mathematical solution using a Wheatstone bridge circuit. By arranging strain gauges in specific orientations and connecting them in a Wheatstone bridge configuration, the system uses electrical signal processing to mathematically separate bending and torsional strain components, eliminating the need for complex mechanical decoupling devices.
2Measurement precision
If pedal-based power measurement approaches are used, then direct power measurement is achieved, but calibration becomes expensive and time consuming
Solution Approach 1:
The patent implements self-service calibration by designing a system that automatically determines calibration factors through operational data analysis. The microcontroller processes strain gauge readings during actual cycling, using known relationships between crank arm geometry, rider mass, and gravitational force to calculate calibration constants without requiring external calibration equipment or technician intervention.
Solution Approach 2:
The patent changes the calibration approach from fixed manufacturer-performed calibration to dynamic operational calibration. The system measures multiple parameters (strain gauge outputs, crank arm angle, cadence, rider mass) and uses these varying parameters during normal operation to derive calibration factors, transforming calibration from a static setup task to an adaptive operational process.
3Measurement precision
If multiple strain gauges are used to decouple bending and torsion strains, then measurement accuracy improves, but manufacturing cost increases
Solution Approach 1:
The patent applies universality by designing a crank arm structure that serves multiple functions: it acts as both the structural component transmitting pedal forces and as the mounting platform for the strain gauge measurement system. The integrated design eliminates the need for separate measurement devices, reducing overall manufacturing cost while maintaining measurement accuracy through the multi-oriented gauge arrangement.
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 solution provides a low-cost, accurate, and direct power measurement system that effectively decouples torsional and bending strains, reducing calibration costs and complexity, enabling a simple and cost-effective power meter for human-propelled vehicles.
Implementation Method 1
The pair of strain gauges are mounted to the spindle (shaft) in a shear pattern to measure shear strain in a direction perpendicular to a radius of the spindle (shaft)
Implementation Method 2
electrically connected in a Wheatstone Bridge arrangement to measure shear strain from torsional forces whilst negating shear strain from bending forces
Implementation Method 3
A torque sensor with a spindle and pair of strain gauge grids mounted in a shear pattern, electrically connected in a Wheatstone Bridge arrangement to measure shear strain
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A torque sensor (26) for a human-powered object includes a spindle (50) connecting crank arms (16) of the object. In one embodiment, the object can be a bicycle. The torque sensor (26) further includes at least one strain gauge (52, 54) mounted to the spindle (50) in a shear patterns to measure strain perpendicular to a radius of the spindle (50) and electrically connected in a Wheatstone Bridge arrangement to measure shear strain from torsional forces whilst negating shear strain from bending forces.