Planar Eddy Current Coil Layout for Tilt-Accurate Linear Sensing
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Solution Overview
Problem
Existing linear displacement sensors for shock absorbers require large wire coils, involve analogue signal handling, necessitate additional printed circuit boards, and have high assembly efforts, while being susceptible to tilt errors and lateral displacements due to air gaps.
Innovation Solution
An Eddy current sensor device utilizing a planar coil configuration with odd-numbered turns and a microcontroller for signal evaluation, eliminating the need for separate coils and analogue components, and compensating for tilt errors through symmetrical coil arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large wire coils are used for sensing, then the measurement range is sufficient, but the device size and assembly complexity increase
Solution Approach 1:
The patent combines multiple coils into a single planar coil structure with odd-numbered turns. The planar coil integrates both primary and secondary winding functions in one component, eliminating the need for separate coil assemblies and reducing overall device complexity while maintaining adequate measurement range.
Solution Approach 2:
The patent replaces traditional wire coil winding with a planar printed circuit board (PCB) trace structure. This substitution eliminates manual coil winding processes, reduces assembly steps, and allows for automated PCB manufacturing while maintaining the electromagnetic sensing function.
2Reliability
If separate coils and analogue components are used, then the sensing function is achieved, but the number of parts and assembly effort increase
Solution Approach 1:
The patent merges the sensing coil and evaluation electronics into a single integrated circuit board. The planar coil is printed directly on the PCB along with the evaluation circuitry, eliminating the need for separate coils, analog components, and multiple connection points, thereby reducing the total part count while maintaining full sensing functionality.
3Measurement precision
If symmetrical coil arrangements are used, then tilt errors are compensated, but the coil structure becomes more complex
Solution Approach 1:
The patent uses an odd number of turns in the planar coil (e.g., 3, 5, or 7 half-periods) to create an asymmetric structure that inherently compensates for tilt errors. This asymmetric odd-turn design allows the sensor to differentiate between actual displacement and tilt-induced signal changes, providing tilt compensation without requiring complex symmetrical multi-coil arrangements.
4Measurement precision
If planar coil configuration with odd turns is used, then tilt error compensation is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent replaces mechanical coil winding with PCB trace fabrication. The planar coil geometry is defined by standard PCB manufacturing processes (photo lithography, etching), which provide consistent and repeatable dimensions. This substitution reduces sensitivity to manual winding variations and allows for tighter tolerances through automated manufacturing processes.
Solution Approach 2:
The patent changes the coil geometry from traditional circular windings to a planar meandering trace pattern with odd-numbered half-periods. This parameter change in coil structure enables tilt compensation while being compatible with standard PCB manufacturing capabilities, balancing manufacturing precision requirements with functional performance.
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 compact, robust, and cost-effective sensor integration into shock absorbers, reducing assembly complexity and enhancing measurement accuracy by compensating for tilt errors and lateral displacements.
Implementation Method 1
The fast changing magnetic field created by the AC-powered primary coil causes such currents within the conductor
Implementation Method 2
Eddy currents cause a compensation of an external alternating field. They reduce the magnetic flux through the covered parts of an underlying secondary coil
Implementation Method 3
Ferromagnetic materials concentrate the field and have an inverse effect on the flux in the secondary coil
Data Source
Figure 1
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AI summary
The present invention relates to an eddy current sensor device for measuring a linear displacement of a boundary of a conductive element in a sensing plane. The sensor device (100) comprises a sender member (110) for emitting a magnetic field. Further, the sensor device comprises a central position sensing member (200) for outputting a central position signal dependent on the linear displacement of the boundary of the conductive element, the central position sensing member comprising a pair of central sense coils (210, 220) each being formed by a plurality of turns, wherein the turns of each central sense coil being arranged side by side along a linear axis (X) in the sensing plane thereby covering a measurement range. Further, the sensor device comprises an edge position sensing member (300) for outputting an edge position signal dependent on the linear displacement of the boundary of the conductive element, the edge position sensing member comprising a pair of edge sense coils (310, 320) each being formed by a plurality of turns, the turns of each edge sense coil being arranged side by side along the linear axis in the sensing plane for increasing the measuring accuracy of the measurement range. Further, the number of turns of each of a central sense coils and the edge sense coils is odd.