Spool Position Sensing With Differential Coils for Flow Control Valves
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Solution Overview
Problem
Conventional spool position detection devices for flow rate control valves face challenges such as mechanical durability issues, high maintenance requirements in contaminated environments, and the need for different sensors for varying spool stroke lengths, which increase complexity and manufacturing costs.
Innovation Solution
A spool position detection device using a magnetically-responsive target probe and two coils with adjustable impedance, allowing for contactless position detection with temperature compensation, enabling a single sensor housing to accommodate various spool stroke lengths and reducing manufacturing costs by eliminating the need for multiple sensor types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electric resistance type position detector using a potentiometer is used, then the structure is simple and manufacturing cost is low, but durability is poor due to mechanical contacts
Solution Approach 1:
The patent replaces the mechanical contact-based potentiometer with an electromagnetic sensing system consisting of coils and a magnetic target probe. This substitution eliminates mechanical wear and contact degradation, significantly improving durability while maintaining a relatively simple overall structure through the use of standard electromagnetic components.
Solution Approach 2:
The patent introduces a magnetic target probe as an intermediary between the spool and the coils. This magnetic intermediary enables contactless detection of spool position by translating mechanical displacement into magnetic field variations, thereby avoiding direct mechanical contacts while keeping the system structure simple.
2Reliability
If an optical type position detector is used, then position detection is contactless, but maintenance requirements increase in contaminated environments
Solution Approach 1:
The patent replaces optical detection with electromagnetic detection using coils and a magnetic target probe. This substitution makes the system inherently more robust in contaminated environments because electromagnetic fields are not affected by dust, oil, or other contaminants that would obstruct or degrade optical paths, thereby reducing maintenance requirements.
3Measurement precision
If an electromagnetic type position detector with AC-energized coil is used, then position detection is contactless and durable in contaminated environments, but coil impedance variation due to temperature characteristics reduces detection accuracy
Solution Approach 1:
The patent uses parameter changes in the magnetic target probe's geometry (gradually varying cross-sectional area) to compensate for temperature-induced impedance variations in the coils. By carefully designing the magnetic circuit parameters, the system maintains accurate position detection across a range of temperatures despite coil impedance drift.
4Adaptability or versatility
If different position sensors are prepared for various models of flow rate control valves with different spool stroke lengths, then detection accuracy is maintained, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent designs a universal position detection system where the same coil assembly and magnetic target probe configuration can detect spool positions across different stroke lengths. The magnetic target probe's gradually varying cross-section and the coils' positioning enable accurate detection whether the spool travels a short or long distance, eliminating the need for model-specific sensors and reducing overall system complexity.
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 accurate, durable, and cost-effective spool position detection across different spool stroke lengths, ensuring high accuracy and linearity of measurement while minimizing the impact of temperature drift and environmental contamination.
Implementation Method 1
first and second coils (C1, C2) provided around the outer periphery of the cylinder section (33) and axially spaced from each other by a predetermined distance (d)... the impedance of the first coil (C1) varies in response to a changing position of the target probe (31)... the impedance of the second coil (C2) does not vary in response to a linear position of the target probe (31)
Implementation Method 2
a generally straight target probe (31) formed of a magnetically-responsive substance... the impedance of the first coil (C1) varies in response to a changing position of the target probe (31)
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
Flow rate control valve includes: a target probe (31) formed of a magnetically-responsive substance and mounted to one end of a spool (12); a sensor housing (32) mounted to the one end of the sleeve and having a cylinder section (33) defining an inner space to permit entry therein of the target probe (31); and first and second coils (C1, C2) provided around the cylinder section and axially spaced from each other by a predetermined distance. The probe is constructed in such a manner that magnetic response of the coils gradually varies in one direction in response to a linear position of the target probe. The first coil (C1) is provided so as to respond to the target probe, while the second coil (C2) is provided so as not to respond to the target probe. Impedance of the first coil varies in response to a linear position of the probe (31), and the linear position of the probe is detected through differential synthesis performed between outputs of the first and second coils.