Electric Motor Eccentricity Detection Using Apparent Resistance
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Solution Overview
Problem
Existing methods for detecting static and dynamic eccentricities in electric motors are inaccurate, costly, and difficult to implement, particularly due to interference from controller types and the inability to distinguish between static and dynamic eccentricities, leading to vibration and noise issues.
Innovation Solution
A method and device that analyze voltage and current waveforms to determine static and dynamic eccentricities by calculating apparent resistance variations, using techniques such as heterodyne demodulation and low-pass filtering, allowing for clear estimation of eccentricity levels regardless of controller structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical micrometers are used to detect motor shaft movement for determining eccentricity, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces optical measurement systems with electrical signal analysis. By analyzing current waveforms and extracting fault signatures through signal processing techniques, the system achieves eccentricity detection without mechanical or optical sensors, thereby reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent uses electrical current signals as an intermediary to indirectly measure eccentricity. Instead of directly measuring shaft position with optical micrometers, the system detects changes in current waveforms caused by eccentricity-induced variations in air gap and magnetic flux, providing a non-intrusive measurement approach
2Object-affected harmful factors
If accelerometers and acoustic sensors are used to detect vibrations, then vibration level detection is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical vibration sensors (accelerometers) with electrical signal analysis. By processing motor current signals to extract vibration-related fault signatures, the system detects vibration effects through electrical domain analysis, eliminating the need for separate mechanical sensing equipment
Solution Approach 2:
The patent combines vibration detection functionality with the existing motor control system. The same current sensors used for motor control are also utilized for eccentricity and vibration detection through signal processing, merging multiple functions into a single system and avoiding additional equipment
3Difficulty of detecting and measuring
If Motor Current Signal Analysis (MCSA) is used to detect fault signatures, then detection capability is improved, but the ability to distinguish between static and dynamic eccentricity deteriorates
Solution Approach 1:
The patent segments the fault detection process into distinct analysis pathways for static and dynamic eccentricity. By applying specific signal processing techniques and analyzing different spectral components of the current signal, the system separately identifies and quantifies each eccentricity type, preventing information loss and enabling differentiated diagnosis
Solution Approach 2:
The patent transitions from frequency-domain analysis alone to a multi-dimensional approach combining time-frequency analysis and spectral analysis. This dimensional expansion allows the system to extract both the presence and type of eccentricity from the current signal, recovering information that would be lost in conventional single-domain analysis
4Ease of operation
If closed loop current controller is used to produce perfect current sinewaves, then current quality is improved, but the level of harmonic produced by eccentricity is reduced, affecting fault detection
Solution Approach 1:
The patent recognizes that the current controller's harmonics, while masking eccentricity signals, also provide a reference for detection. By analyzing the relationship between controller-generated harmonics and actual current harmonics, the system can identify eccentricity-induced deviations even in the presence of high-quality current waveforms
Solution Approach 2:
The patent employs feedback mechanisms where the known characteristics of the current controller are used as a reference. By comparing actual current waveforms against expected waveforms from the controller model, the system can detect deviations caused by eccentricity, effectively using the controller's own output as a detection reference
Data Source
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AI summary
The invention concerns a device and a method for determining static and dynamic eccentricities of and electric motor. The invention: - obtains voltage and current waveforms of the electric motor; - obtains a waveform representative of an apparent resistance of the motor from the obtained voltage and current waveforms; - determines an average value (RDC) and an oscillating component value (ΔRfr) of the apparent resistance of the motor from the obtained waveform representative of the apparent resistance of the motor; - determines a reference apparent resistance value (Ro) expected in absence of eccentricity; - determines static and dynamic eccentricities from the determined average value and the determined oscillating component value of the apparent resistance of the motor and from the determined reference apparent resistance of the motor.