Linear Inductive Position Sensor with Harmonic-Canceling Coils
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Solution Overview
Problem
Conventional linear inductive position sensors face challenges in maintaining primary signal strength while minimizing harmonic signals and reducing cross-talk signals, particularly when the air gap between the target coil and the PCB changes, affecting positional accuracy.
Innovation Solution
The implementation of a linear inductive position sensor with multiple receiver coils configured in twisted loop geometries and offset distances, combined with a Vernier processor, to cancel specific harmonics and enhance positional accuracy by using dual sensor systems with distinct loop offsets and phase configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the air gap between the target coil and PCB is narrowed to increase signal strength, then the primary signal strength increases, but harmonic signals increase affecting positional accuracy
Solution Approach 1:
The receiver coil is segmented into multiple discrete receiver coils (first receiver coil, second receiver coil, third receiver coil) positioned at different locations. Each coil detects different harmonic components, allowing the system to segment the signal detection function and process different frequency components separately to eliminate harmonics while maintaining primary signal strength.
Solution Approach 2:
A Vernier processor acts as an intermediary between the multiple receiver coils and the final position determination. The processor receives signals from multiple coils, processes them to eliminate harmonic components, and generates the final position signal, thereby mediating between the raw signals and the required clean position data.
2Measurement precision
If multiple receiver coils are added to cancel harmonics, then positional accuracy improves, but device complexity increases
Solution Approach 1:
Multiple receiver coils are merged into a single integrated coil structure formed on the PCB substrate. The coils are electrically connected and physically integrated within the same sensor assembly, combining the functionality of multiple detection elements while maintaining a compact form factor and avoiding the complexity of separate sensor units.
Solution Approach 2:
The multiple receiver coils serve multiple functions simultaneously: they detect the primary signal, detect different harmonic components, and enable the system to cancel harmonics through differential processing. This multi-functionality allows a single sensor structure to perform what would traditionally require separate components.
3Power
If the target coil width is increased to improve signal strength, then the primary signal increases, but cross-talk signals between adjacent coils increase
Solution Approach 1:
Each receiver coil is designed with specific local characteristics - different positions, different orientations, and different functional assignments. The first receiver coil is positioned to detect primary signal, the second to detect harmonics, and the third to detect additional signal components. This local differentiation allows each coil to optimize its detection while minimizing interference with others.
Solution Approach 2:
The receiver coils are arranged in an asymmetric configuration rather than symmetric positioning. The coils are placed at specific non-uniform locations on the PCB to optimize their detection characteristics and minimize cross-talk. This asymmetric arrangement allows differential processing to effectively cancel harmonics and cross-talk signals while maintaining strong primary signal detection.
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
This approach effectively cancels harmonics such as third, fifth, and seventh harmonics, allowing for high-accuracy position sensing with minimal interference, enabling precise determination of the target's position within a narrow air gap.
Implementation Method 1
an excitation coil configured to generate an electromagnetic field when an electrical alternating current (AC) flows through the coil, a receiving coil configured to detect an electrical potential, a voltage, induced in the receiving coil by the currents flowing through the excitation coil
Implementation Method 2
The inductive coupling between the excitation coil, target, and the receiving coil may be expressed by a series of mathematical functions (each a 'transfer function')
Data Source
AI summary
A position of a target is determined using a linear inductive position sensor that includes a target coil, an excitation coil, two sensors and a Vernier processor. The sensors each include two or more receive coils. The receive coils include multiple twisted loops. In the first sensor, the coils have a first period, with loops offset by first distance. In the second sensor, the coils have a second period, with loops offset by a second distance. The target coil width is a function of the first distance and the second distance. During operation, the coils output voltages in which third, fifth and/or seventh harmonics are cancelled. Based on the voltages, the sensors output respective first and second position signals, from which the Vernier processor calculates the target's position along an axis of the position sensor.