Hollow Crank Axle Torque Sensor with Wireless Signal Extraction
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Solution Overview
Problem
Existing systems for measuring pedaling torque and power in cycling are prone to measurement errors due to assumptions of constant angular velocity and torque, particularly when using metallic bicycle components that interfere with radiofrequency signal transmission, leading to inaccurate power calculations and loss of biomechanical information about individual leg contributions.
Innovation Solution
A torque and power sensor device featuring a hollow crank axle with strain sensors on its surface or inside, connected to an electronic control unit that calculates and wirelessly transmits pedaling parameters, including cadence and crank angular position, using a radiofrequency antenna to overcome signal shielding by metallic components and provide precise measurements of torque and power distribution between legs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain sensors are placed on metallic bicycle components (crank axle, spider, chainrings), then torque measurement is achieved, but radiofrequency signal transmission is blocked leading to inaccurate power calculations
Solution Approach 1:
The electronic control unit and antenna are extracted from the metallic crank axle and placed in a separate non-metallic location (handlebar or frame). This removes the source of radiofrequency signal transmission away from the metallic components that cause shielding, allowing accurate wireless communication while maintaining torque measurement capability through the strain sensors on the crank axle.
Solution Approach 2:
A non-metallic transmission path is introduced as an intermediary between the electronic control unit and the external receiver. The signal is transmitted through air space rather than through metallic components, eliminating the shielding effect while maintaining data transmission functionality.
2Device complexity
If angular velocity is assumed constant for each revolution, then power calculation is simplified, but measurement error increases due to variable pedaling conditions
Solution Approach 1:
The system transitions from assuming constant angular velocity to dynamically measuring and using the actual variable angular velocity at each instant. The electronic control unit calculates real-time angular velocity based on strain sensor data and crank position, allowing accurate power calculation that adapts to changing pedaling conditions while maintaining reasonable computational complexity.
3Quantity of substance
If total torque from both legs is measured at the spider, then overall power is obtained, but individual leg biomechanical information is lost
Solution Approach 1:
The measurement system is segmented to measure each crank arm independently. Strain sensors are placed on both the left and right crank arms separately, allowing the electronic control unit to calculate individual torque and power for each leg. This segmentation preserves individual leg biomechanical information while still providing total power measurement by summing both sides.
4Measurement precision
If strain sensors are placed on the crank axle to measure torque, then torque data is obtained, but the metallic structure shields radiofrequency signals from transmission
Solution Approach 1:
The electronic control unit containing the radiofrequency antenna is extracted from the metallic crank axle structure and relocated to a non-metallic position (handlebar or frame). This maintains the torque measurement capability through strain sensors on the crank axle while eliminating radiofrequency signal shielding by removing the transmission electronics from the metallic environment.
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 accurate, high-resolution measurements of pedaling torque and power, minimizing errors associated with variable angular velocity and oval chainrings, and offers detailed biomechanical insights into leg contributions, enhancing training and performance analysis.
Implementation Method 1
strain sensors placed either on the spindle outside surface or on the spindle inside surface, in order to measure its torsional deformation and directly calculate the torque applied by the cyclist left leg
Data Source
AI summary
A torque and power measuring device corresponding to the non-drive side cyclist leg, comprising a hollow shaft connecting the two bicycle crank arms with strain sensors arranged in the shaft surface. These sensors are connected to an electronic control unit housed inside the shaft, to which are also connected other different sensors to measure a plurality of interesting quantities (pedaling cadence, crank arm angular position . . . ). This electronic control unit picks the sensor signals up, stores them and performs pre-programmed software operations to later wirelessly output the result signals towards a receiving device for analysis and/or storage them, by means of an antenna located outside the shaft and anchored to the outer surface of the jointed crank arm with the shaft.