Magnetic Bearing Digital Signal Processing Offset Control
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Solution Overview
Problem
Conventional magnetic bearing devices require frequent offset adjustments due to changes in floating capacitance, leading to increased circuit size and reduced magnetic levitation controllability, especially when using low carrier wave frequencies to avoid phase delay.
Innovation Solution
The magnetic bearing device employs a digital signal processing system with a sampling frequency set to 4/3 or 4/5 times the carrier frequency, allowing for higher sampling without aliasing and reducing digital calculation processing size, while using phase shifting and low-pass calculation to demodulate and control the excitation amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the frequency of the carrier wave is set low to avoid phase delay, then magnetic levitation controllability is maintained, but the circuit size increases due to the need for multiple notch filters
Solution Approach 1:
The patent replaces the mechanical analog filtering system (multiple notch filters) with a digital signal processing system. The A/D conversion means converts the sensor signal to digital form, and the digital filter means performs filtering operations in the digital domain, eliminating the need for complex analog filter circuits while maintaining the required frequency characteristics and controllability
Solution Approach 2:
The patent changes the operating parameters by using digital signal processing with specific sampling frequencies (4/3 or 4/5 times the carrier frequency) to achieve the desired filtering effect without requiring multiple analog notch filters, thereby reducing circuit complexity while maintaining controllability
2Reliability
If the frequency of the carrier wave is set low to avoid phase delay, then magnetic levitation controllability is maintained, but offset adjustment becomes necessary more frequently due to floating capacitance changes
Solution Approach 1:
The patent replaces the analog sensor signal processing system with a digital system. The A/D conversion means and digital filter means process the sensor signal in the digital domain, making the offset adjustment independent of floating capacitance changes in the cable and sensor connections, thereby eliminating the need for frequent manual offset adjustments
Solution Approach 2:
The digital signal processing system automatically handles offset compensation through digital filtering and processing, eliminating the need for manual intervention. The system self-adjusts to floating capacitance changes without requiring operator attention, improving ease of operation
3Measurement precision
If a large number of notch filters are used instead of a low-pass filter, then phase delay of the required band is avoided, but the circuit size increases
Solution Approach 1:
The patent replaces the complex analog filter network (multiple notch filters) with a digital filter implemented in the digital signal processing system. The digital filter achieves the required phase characteristics and frequency selectivity through software algorithms, eliminating the need for multiple physical filter components and reducing circuit size
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 approach eliminates the need for frequent offset adjustments, reduces circuit size, and maintains magnetic levitation controllability by setting the sampling frequency within specific bands, enabling efficient digital processing without aliasing.
Implementation Method 1
A carrier wave is applied to the displacement sensor, and the carrier wave is amplitude modulated by change of impedance of the sensor part due to change of gap with the rotating body.
Implementation Method 2
an electromagnet for contactlessly supporting a supported body
Data Source
AI summary
An electromagnet configured to contactlessly support a body includes an excitation amplifier configured to supply excitation current to the electromagnet, a carrier wave generation device, and a sensor configured to modulate the carrier wave and to output a sensor signal. An A/D conversion device is included for converting the sensor signal to a digital signal at a sampling frequency such that the frequency range of the sensor signal is either higher than 1/2 times the sampling frequency and lower than the sampling frequency, or higher than the sampling frequency and lower than 3/2 times the sampling frequency. In addition, a demodulation calculation device for demodulating the digitized sensor signal and a control device for controlling the excitation amplifier are provided.