Spindle Load Cell Layout for Precise E-Bike Torque Sensing
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Solution Overview
Problem
Existing systems for measuring external forces in electric bicycles lack accuracy and reliability, particularly in determining torque and angle of rotation, leading to inefficiencies in controlling the electric motor assistance.
Innovation Solution
A motor unit with a load cell and strain gauges on flaps arranged radially on a support ring, combined with an evaluation unit, measures resistance to determine external force and torque, using redundant measurements and filtering techniques to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a load cell with strain gauges is used to measure external force, then measurement capability is provided, but measurement precision and reliability are insufficient
Solution Approach 1:
The measurement system is segmented into multiple independent strain gauges (first strain gauge and second strain gauge) positioned at different locations on the support ring. Each strain gauge independently measures force components, and the evaluation unit processes these separate measurements to determine the total external force, thereby improving both precision and reliability through distributed measurement points.
Solution Approach 2:
Different strain gauges are positioned at specific locations on the support ring to measure different aspects of the external force. The first strain gauge measures force in one radial direction while the second strain gauge measures force in another radial direction, creating local measurement zones that collectively provide comprehensive and precise force measurement.
2Measurement precision
If separate measurements of both strain gauges are performed, then measurement accuracy is improved, but evaluation process complexity increases
Solution Approach 1:
The evaluation unit merges the separate measurements from the first and second strain gauges into a unified torque calculation. By combining the resistance values from both strain gauges according to their respective positions on the support ring, the system achieves accurate torque measurement while maintaining a relatively simple evaluation process that processes multiple inputs into a single output value.
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 system provides precise and reliable measurements of external forces and torques, improving the efficiency and control of the electric motor assistance by reducing errors and simplifying the evaluation process.
Implementation Method 1
Depending on a change of length of the first flap or the second flap due to a material expansion, the first strain gauge and/or the second strain gauge change their respective resistance
Data Source
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AI summary
An external force measurement unit 4 for measuring an external force fe applied to a spindle 10 includes a load cell 5 with a support ring 61, wherein a first flap 62 and a second flap 65 are arranged on the support ring 61, wherein the second flap 65 is arranged opposite to the first flap 62 on the support ring 61, wherein each flap is arranged in a radial direction towards the outside of the support ring 61, a first strain gauge 64, which is arranged on the first flap 62, and a second strain gauge 67, which is arranged on the second flap 65, an evaluation unit 14 for measuring the resistance of the first strain gauge 64 and the resistance of the second strain gauge 67, wherein the resistance of the first strain gauge 64 is measured separately from the resistance of the second strain gauge 67, a first bearing support 6 for taking up a first bearing 7 in a first bearing seat 68, wherein the first bearing 7 is adapted to take up a rotating spindle 10, wherein the evaluation unit 14 is configured to determine the external force fe based on the resistance of the first strain gauge 64 and the resistance of the second strain gauge 67.