Hollow Plunger Core Inductive Sensor Cost Reduction
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Solution Overview
Problem
Inductive position sensors face high costs due to the use of expensive soft magnetic materials, particularly in the plunger core, which constitutes a significant portion of the total sensor cost, and existing solutions have not adequately addressed this issue while maintaining accuracy.
Innovation Solution
The design incorporates a hollow circular plunger core and outer shielding made from electrical steel, with a thin-walled soft magnetic tubular shield and a shield hole washer element, minimizing the use of expensive materials and leveraging the skin-effect to maintain inductance change efficiency, allowing for a cost reduction without compromising accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a solid plunger core made from soft magnetic material (iron alloy) is used, then the position detection accuracy is maintained, but the cost increases significantly (over 10-15% of total sensor cost)
Solution Approach 1:
The plunger core is divided into two distinct parts: an inner solid core made from inexpensive non-magnetic material (plastic, aluminum, or steel) and an outer hollow cylindrical shell made from thin electrical steel foil (0.05-0.5mm thick). This segmentation allows the expensive soft magnetic material to be used only where it is most effective for inductance change, while the bulk of the plunger core uses cheap material for structural support, reducing overall cost while maintaining detection accuracy.
Solution Approach 2:
The plunger core employs a composite structure combining non-magnetic structural material (for mechanical strength and support) with a thin layer of electrical steel foil (for magnetic functionality). This composite approach leverages the advantages of both material types: the inexpensive structural material provides mechanical integrity, while the thin magnetic foil maintains the necessary inductance modulation capability, achieving cost reduction without sacrificing performance.
2Quantity of substance
If electrical steel is used in the plunger core, then the cost is reduced, but the manufacturing complexity increases due to the need for hollow cylindrical form and thin-walled construction
Solution Approach 1:
The patent utilizes thin electrical steel foil (0.05-0.5mm thick) to form the hollow cylindrical shell of the plunger core. This thin-film approach reduces material cost and weight while the foil can be easily formed into the required cylindrical shape through conventional manufacturing processes. The thin-walled construction maintains magnetic effectiveness while simplifying manufacturing compared to traditional solid cores.
Solution Approach 2:
A supporting structure or mandrel is used as an intermediary during the manufacturing process to form the hollow cylindrical electrical steel shell. This intermediary supports the thin foil during forming and assembly, enabling the creation of the complex hollow geometry without requiring complex direct manufacturing processes. The supporting structure is removed or remains as part of the final assembly, facilitating easier production of the thin-walled plunger core.
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 design reduces the cost of the plunger core to less than 10% of the conventional solid iron plunger core cost, achieving cost efficiency while maintaining position detection accuracy, and allows for bulk purchasing of inexpensive electrical steel strips for multiple parts.
Implementation Method 1
The coil when connected to an alternating voltage source produce a magnetic field and acts as a magnet
Implementation Method 2
the plunger core is made of soft magnetic material that change the inductance in the coil
Implementation Method 3
leveraging the skin-effect to maintain inductance change efficiency
Data Source
Figure 1a~1c
Figure 2~3
Figure 4a~4b
AI summary
The invention relates to an inductive position sensor, comprising: a first part with a cylindrical coil winding (14) having a longitudinal direction, a second part with a soft magnetic plunger core (20). The invention also relates to the soft magnetic plunger core and a magnetic shield around said cylindrical coil winding for said inductive position sensor. According to the invention is the soft magnetic plunger core as well as the magnetic shield hollow, preferably with circular cross-section, and made from electrical steel or soft iron sheet material.