Capacitive Air-Gap Sensing in Magnetic Bearings Without Active Shielding
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Solution Overview
Problem
Commercially available capacitive sensors for magnetic bearings are expensive, require complex mechanical structures, and have large dimensions due to tri-axial cables and active shielding, which complicates their integration in high-cleanliness and in-vacuum systems.
Innovation Solution
A capacitive sensor device with a frequency-dependent input signal generator and operational amplifier configuration, allowing the sensor's measurement surface to be at virtual ground potential, eliminating the need for active shielding and enabling the use of coaxial cables, thereby simplifying the design and reducing complexity and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commercially available capacitive sensors are used for air gap measurement in magnetic bearings, then measurement accuracy is improved, but device complexity and cost increase due to tri-axial cables and active shielding
Solution Approach 1:
The patent extracts and removes the active shielding component from the capacitive sensor assembly, retaining only the essential measurement elements (capacitive sensor and coaxial cable). This elimination of the active shielding subsystem reduces structural complexity while preserving measurement functionality through the simplified coaxial cable configuration.
Solution Approach 2:
The patent replaces expensive, complex tri-axial cable assemblies with simpler, more economical coaxial cables. This substitution uses a less complex, more cost-effective cable type that achieves the same electrical function without requiring the three-conductor configuration of tri-axial cables, thereby reducing overall system cost and complexity.
2Object-affected harmful factors
If commercially available capacitive sensors with tri-axial cables are used, then shielding effectiveness is improved, but sensor dimensions and system size increase
Solution Approach 1:
The patent substitutes the mechanical tri-axial cable system with an electrical solution using a coaxial cable. The coaxial cable's inherent electromagnetic shielding properties replace the need for the complex tri-axial cable structure, achieving equivalent or superior EMI protection while significantly reducing cable diameter and sensor assembly size.
3Reliability
If active shielding is implemented in capacitive sensors, then measurement reliability is improved, but energy dissipation increases
Solution Approach 1:
The patent employs the coaxial cable's inherent electromagnetic shielding properties as a passive, self-sufficient solution. The coaxial cable structure naturally provides EMI protection through its geometric configuration and electromagnetic field distribution, eliminating the need for active shielding components that require external power and control circuits, thereby reducing energy dissipation.
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 reduces hardware costs, minimizes energy dissipation, and allows integration within the magnetic bearing airgap, improving system performance and suitability for vacuum environments by using passive shielding and smaller diameter cables.
Implementation Method 1
a capacitive sensor component (110) with a first sensor node (110a) mounted to the target rigid body (20) and a second sensor node (110b) mounted to the other rigid body (30)
Implementation Method 2
a frequency-dependent input signal generator (130) being operatively connected to the first sensor node (110a) of the capacitive sensor component (110) and being structured to apply a frequency-dependent voltage signal (Vosc) to the target rigid body (20)
Implementation Method 3
a transmission component (120) having at least a first input node (120a) and an output node (120b) for providing an output signal (Vout) representative of the distance (g1) between the two rigid bodies (20, 30)
Data Source
AI summary
The invention relates a capacitive sensor device for determining a distance between a rigid body and another rigid body in a system for contactless linear displacement along a linear displacement path of the rigid body relative to the other rigid body, the capacitive sensor device comprising a capacitive sensor component with a first sensor node mounted to the rigid body and a second sensor node mounted to the other rigid body; a transmission component having at least a first input node for receiving an input signal as well as an output node for providing an output signal representative of the distance; a frequency-dependent input signal generator operatively connected to the first sensor node of the capacitive sensor component and the first input node of the transmission component being operatively connected to the second sensor node of the capacitive sensor component.