Position Detector Fourier Analysis Offset Correction
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Solution Overview
Problem
Conventional position detectors with sinusoidal output signals for high-speed rotation shafts face accuracy degradation due to high-frequency signals, limiting their performance in high-speed applications.
Innovation Solution
Quantitative determination of offset, phase difference, and amplitude ratio components using Fourier analysis of Lissajous circle radius values, allowing for precise correction and improved interpolation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor with small pitch is used to improve interpolation accuracy, then position detection accuracy is improved, but the signal frequency becomes excessively high at high rotational speeds
Solution Approach 1:
The patent changes the pitch parameter of the position sensor from small to large (e.g., from 10 degrees to 30 degrees), which allows high-speed rotation while maintaining adequate position detection capability. The Fourier analysis technique compensates for the reduced inherent accuracy by correcting interpolation errors.
Solution Approach 2:
The patent introduces Fourier analysis as an intermediary processing step between the position sensor and the control system. This intermediary technique analyzes the sinusoidal signals to determine offset, amplitude ratio, and phase difference, then uses this information to correct interpolation errors, enabling accurate position detection at high speeds.
2Speed
If a position sensor with large pitch is used to enable high-speed rotation, then rotational speed capability is improved, but interpolation accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where Fourier analysis continuously determines the actual offset, amplitude ratio, and phase difference from the sinusoidal signals, then uses this feedback information to correct the interpolation calculations. This feedback loop maintains high interpolation accuracy even with large pitch sensors operating at high speeds.
Solution Approach 2:
The patent replaces the mechanical solution of using small-pitch sensors (which physically limit high-speed operation) with a signal processing approach using Fourier analysis. This substitution allows the use of large-pitch sensors while maintaining accuracy through mathematical correction rather than physical constraints.
3Speed
If conventional position detection methods are used at high rotational speeds, then high-speed operation is enabled, but position detection accuracy is limited
Solution Approach 1:
The patent performs preliminary Fourier analysis to determine the offset, amplitude ratio, and phase difference before conducting position detection. This preliminary characterization of the sinusoidal signals allows the system to pre-calculate correction factors that are then applied during high-speed operation, ensuring accurate position detection from the start.
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
Enhances interpolation accuracy and enables simultaneous high accuracy and high speed in position detection by accurately identifying and eliminating degrading components at each rotational position.
Implementation Method 1
a position sensor which outputs two signals that sinusoidally vary at a pitch of wavelength λ with respect to a measured displacement and have phases shifted from each other by 90 degrees
Implementation Method 2
components that degrade the interpolation accuracy such as an offset, phase difference, and amplitude ratio are quantitatively determined based on a value obtained by performing a Fourier analysis
Data Source
Figure 1
Figure 2~3
AI summary
Two position sensors provide, as outputs, two signals that vary sinusoidally at a pitch of wavelength λ with respect to a displacement of a target and have phases shifted from each other by 90°. A memory unit has stored therein offset values for the two signals, and two subtractors eliminate the offset values from the two signals, respectively. The two signals after offset elimination are converted into position data in an interpolation calculator. A radius calculator calculates a radius value of the two signals after offset elimination. An FFT calculates offset values based on the position data and the radius values, and the calculated offset values are used to update the values stored in the memory unit. An amplitude ratio correction value and a phase difference correction value for the two signals are updated similarly. By performing elimination of the components that degrade interpolation accuracy at every rotational position, interpolation accuracy is improved.