Toroidal Coil Position Sensor with Closed Magnetic Circuit
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Solution Overview
Problem
Existing devices for measuring relative positions using deformable coils suffer from inaccuracies due to stray magnetic fields, which complicate the proportionality between shape change and inductance change, and result in reduced measurement accuracy and susceptibility to environmental influences.
Innovation Solution
A device employing a toroidal coil with a closed magnetic circuit, either as a ring coil or formed by parallel helical springs connected by magnetically conductive bridges, eliminates stray fields, ensuring a linear relationship between inductance and shape change, thereby enhancing measurement accuracy and reducing interference emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If air-core helical springs are used as coils, then the construction is simple, but stray magnetic fields occur that reduce measurement accuracy
Solution Approach 1:
A magnetic shielding element (intermediary component) is introduced between the air-core helical spring coil and the surrounding environment. This shielding element redirects the stray magnetic field lines, preventing them from forming external interference fields while maintaining the simple air-core construction. The shielding element acts as a mediator that resolves the contradiction by containing the magnetic flux without complicating the basic coil structure.
2Device complexity
If air-core coils are used, then the device construction is simple, but external electromagnetic influences and permeability variations affect measurement reliability
Solution Approach 1:
The magnetic shielding element serves as an intermediary that isolates the air-core coil from external electromagnetic influences. It creates a controlled magnetic environment by containing flux lines within the shielding structure, thereby protecting the measurement system from external interference while preserving the simplicity of the air-core construction.
Solution Approach 2:
The magnetic shielding element is integrated with the coil assembly, combining the simple air-core coil structure with flux containment functionality. This merging allows the system to maintain structural simplicity while gaining immunity to environmental magnetic influences through the combined shielding-coil assembly.
3Adaptability or versatility
If helical springs are deformed, then relative position measurement is enabled, but the stray field causes non-linear inductance changes
Solution Approach 1:
The magnetic shielding element acts as an intermediary that maintains a consistent magnetic environment during spring deformation. By containing the flux lines within the shielding structure, it ensures that inductance changes are solely due to the geometric deformation of the coil, not variations in external flux distribution. This restores the linear relationship between spring deformation and inductance change.
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 significantly improved measurement accuracy and immunity to environmental influences, with negligible external interference and reduced emission of interference fields, resulting in a more reliable and precise measurement of relative positions.
Implementation Method 1
the coil has a magnetic circuit that is closed in the manner of a toroidal coil
Implementation Method 2
use of a toroidal coil or a coil construction closed in the manner of a toroidal coil can prevent the occurrence of a stray field
Implementation Method 3
the inductance of the coil being shape-dependent and thus a measure of the relative position
Implementation Method 4
a deformable coil that is connected to both parts and deforms according to their relative position
Implementation Method 5
The inductance of the coil is used, for example, as the frequency-determining part of an oscillating circuit, the frequency of which is measured
Data Source
Figure 1~2
AI summary
Apparatus (1) for measuring the relative position of two parts (2, 3) with a deformable coil (4), which is connected to both parts (2, 3) and deforms according to their relative position, wherein the inductance (L) of the coil (4) depends on shape and is thus a measure of the relative position, and wherein the coil (4) has a magnetic circuit (7) which is closed in the manner of a toroidal coil.