Fiber-Reinforced Crank Arm Sensor Enclosure
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Solution Overview
Problem
Existing crank arm designs with integrated sensors face issues of mechanical weakening, exposure to external impacts, and aesthetic concerns due to sensor placement, as well as sealing and protection problems when sensors are embedded within the crank arm.
Innovation Solution
A crank arm made of fiber-reinforced plastics with sensors fully enclosed on all sides, eliminating the need for additional protective components and ensuring the sensor is integral to the crank arm body, providing protection and a sleek design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If sensors are mounted on the outer surface of the crank arm, then the sensor is exposed and unprotected against impacts, but the sensor can be easily accessed and installed
Solution Approach 1:
The sensor is nested within a cavity in the crank arm, with the cavity walls providing protective enclosure. This nesting approach protects the sensor from external impacts while maintaining a compact integrated structure.
Solution Approach 2:
A cavity structure serves as an intermediary protective element between the external environment and the sensor. The cavity walls act as a mediator that shields the sensor from impacts while allowing the sensor to remain accessible through the cavity opening.
2Object-affected harmful factors
If sensors are mounted in pockets machined into the crank arm, then the sensor is protected, but the crank arm is structurally weakened and requires extensive machining
Solution Approach 1:
The cavity is formed as an integral part of the crank arm manufacturing process, preparing the protective structure in advance during fabrication. This preliminary action ensures the cavity is already in place to protect the sensor without requiring subsequent weakening modifications.
Solution Approach 2:
The crank arm is constructed using composite materials that allow for integrated cavity formation while maintaining structural strength. The composite structure enables the cavity to be formed without significantly compromising the overall structural integrity of the crank arm.
3Object-affected harmful factors
If sensors are embedded on the inner surface of a hollow crank arm, then the sensor is protected from external impacts, but sealing problems occur and the sensor is only partially protected
Solution Approach 1:
The sensor is extracted from the hollow interior and positioned in a cavity structure that provides complete enclosure. This extraction approach eliminates the sealing problems associated with embedding sensors in hollow arms while maintaining protective coverage.
Solution Approach 2:
The sensor is nested within a cavity structure that provides complete enclosure from all sides. This nesting approach ensures the sensor is fully protected from external impacts while eliminating the sealing issues present in hollow arm embeddings.
4Ease of operation
If sensors are exposed on the crank arm surface, then the sensor is easily accessible, but the aesthetic appearance is adversely affected
Solution Approach 1:
The sensor is nested within a cavity in the crank arm, making it invisible from the exterior while maintaining accessibility through the cavity opening. This nesting approach preserves the aesthetic appearance of the crank arm surface.
Solution Approach 2:
The cavity structure serves as an intermediary that hides the sensor from external view while maintaining functional accessibility. The cavity walls act as a mediator that conceals the sensor's presence while allowing it to remain accessible for operation.
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 results in a lightweight, cost-efficient crank arm with enhanced protection against external impacts and improved aesthetics, while maintaining accurate power measurement capabilities.
Implementation Method 1
the sensors used are usually strain measurement sensors, in particular strain gages, measuring the deformation of the particular component, from which the force exerted on the component can be derived
Implementation Method 2
The rotational frequency of the crank arms, i. e. the pedaling frequency, can be measured, for instance, as described in WO 2008/058164 A2, by a Hall sensor fixed to the crank spider or to the crank arm in connection with a magnet fixed to the bicycle frame
Data Source
AI summary
A power measuring system for an at least partially human powered vehicle or training device with a crank drive, in particular a bicycle, with at least one crank arm of the bicycle being manufactured of fiber-reinforced plastics and the crank arm having a sensor, in particular a strain gage, and with the largest part of the sensor being directly enclosed on all sides by the fiber-reinforced plastics. The force exerted on the respective pedal and from this the torque exerted on the bottom bracket shaft is determined by an electronics unit, which is preferably arranged in a cavity in the bottom bracket shaft, from the signal of sensor. From this, together with the rotational frequency of bottom bracket shaft, which is possibly measured by further sensors or is determined in a calculative way, the power currently generated by the user of the bicycle is determined. The power values can, in particular wirelessly, be sent to a display unit and be displayed thereby in the form of power-related information. The sensors in both crank arms, make it possible to determine the power for the left and the right leg of the cyclist separately.