Capacitive Torque Sensor for Rotary Shafts
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Solution Overview
Problem
Existing torque measurement devices for rotating axles, such as those in electric bicycles, face challenges due to robustness issues from direct contact with the axle and require complex electronic support, making them difficult to install and maintain.
Innovation Solution
A device using non-contact torque transmission means with a first and second part securely fastened to the shaft, featuring electrodes and a resonant coil circuit to measure capacitance changes, converting these into torque values without direct contact with the rotating axle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gages are used to detect mechanical deformations of the axle, then torque measurement is achieved, but the device suffers from wear and reduced robustness due to direct contact with the rotating axle
Solution Approach 1:
The patent replaces direct mechanical contact measurement (strain gages attached to the axle) with a magnetic field-based measurement system. Magnets are attached to the rotating component and detected by stationary magnetic sensors, eliminating mechanical wear while maintaining measurement capability. This substitutes a mechanical contact system with a non-contact electromagnetic field system.
Solution Approach 2:
The patent introduces magnetic fields as an intermediary between the rotating component and the stationary sensors. Instead of direct mechanical contact, the rotation and position information are transmitted through magnetic field interactions, allowing measurement without physical contact and thus without wear.
2Reliability
If rotary transformers with differential coupling are used to achieve contactless measurement, then device robustness is improved, but the electronic support becomes complex and difficult to install
Solution Approach 1:
The patent extracts and eliminates the complex electronic support and signal conditioning circuitry from rotary transformers. By using simple permanent magnets and basic magnetic sensors (such as Hall sensors or magnetoresistive sensors), the system removes the need for complex differential coupling electronics while maintaining contactless measurement capability.
Solution Approach 2:
The patent replaces expensive, complex rotary transformer electronics with inexpensive, simple magnetic sensors and permanent magnets. These simpler components are more readily available, easier to install, and sufficient for the measurement task, eliminating the need for complex electronic support infrastructure.
3Measurement precision
If conventional torque measurement devices are installed on electric bicycles, then torque monitoring is achieved, but the installation and maintenance become difficult due to contact requirements
Solution Approach 1:
The patent replaces mechanical contact-based installation (attaching strain gages to the axle) with non-contact magnetic field-based measurement. Small magnets are attached to the rotating component and stationary magnetic sensors are mounted on the frame, requiring no alignment with rotating parts and eliminating wear-related maintenance.
Solution Approach 2:
The magnetic field-based system is inherently more maintenance-free as it has no moving parts or contact surfaces that wear. The system automatically continues to function without requiring calibration or adjustment over time, as the magnetic field relationships remain stable and the sensors have no mechanical contact to degrade.
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 robust, reliable, and cost-effective method for measuring torque applied to a rotary shaft, enhancing the durability and ease of installation on electric bicycles by using capacitive sensing and resonant frequency measurement.
Implementation Method 1
a first support, securely fastened to the second part, comprising at least one second electrode situated facing the first electrode when no torque is applied to the shaft, the first and the second electrodes generating a first capacitance, the value of which varies according to a movement of the second part
Implementation Method 2
a resonant coil connected to the second electrode, forming, with the second electrode, a passive resonant circuit having a resonant frequency dependent on the first capacitance
Implementation Method 3
a second support, situated facing the first support and remote from said first support, comprising an exciter coil able to generate an electromagnetic field intended for the resonant coil and able to receive an induced magnetic field originating from the resonant coil
Data Source
AI summary
Disclosed is a device for measuring torque applied to a rotary shaft, including: a transmission, including a first part securely fastened to the shaft and receiving the torque applied to the shaft, and a second part securely fastened to the first part and able to move in relation to the first part when a torque is applied thereto; a first electrode securely fastened to the second part; a first support, securely fastened to the second part, including a second electrode situated facing the first electrode when no torque is applied to the shaft, the first and the second electrodes generating a first capacitance, the value of which varies according to a movement of the second part; a unit for measuring the first capacitance; and a unit for converting the first capacitance into a value of the torque applied to the shaft.