Angular Correction for Rotary Encoder Skip Errors
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Solution Overview
Problem
Conventional rotary encoders in surveying instruments experience angular skip errors due to systematic distortion when slit images switch during interpolation calculations, leading to discontinuous angular errors of approximately 0.2 to 0.3 seconds.
Innovation Solution
An angular correction method that determines and records residual curves using polynomials of varying orders to compute tangential slopes and correction quantities, minimizing angular skip by adjusting the measured angle values based on these corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional interpolation calculation is used with fixed model parameters, then calculation simplicity is maintained, but angular skip errors occur during slit image switching
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values in a correction table before actual angle measurement. The CPU performs regression analysis on residuals from the interpolation model, stores optimal parameters and correction data in advance, and then uses this pre-prepared data to correct angular skip errors during slit image switching without real-time complex calculations.
Solution Approach 2:
The patent changes the interpolation model parameters dynamically by introducing correction values based on slit image position. Instead of using fixed model parameters (R, A0, P0), the system adjusts these parameters using correction data stored in the correction table, allowing the interpolation calculation to adapt to different slit image positions and eliminate angular skip discontinuities.
2Measurement precision
If regression analysis is performed on all residual data, then measurement precision improves, but calculation time increases
Solution Approach 1:
The patent segments the residual correction data by creating separate correction tables for different ranges of slit image positions. Instead of performing regression analysis on all residual data uniformly, the system divides the correction data into multiple segments based on position ranges, allowing faster lookup and application of appropriate correction values during angle measurement without processing the entire dataset each time.
Solution Approach 2:
The patent performs regression analysis and generates correction tables in advance during system initialization or calibration phase. This preliminary calculation of correction data eliminates the need for time-consuming real-time regression analysis during actual angle measurements, as the CPU only needs to lookup pre-computed correction values from the stored tables.
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 method significantly reduces angular skip errors, enabling highly precise angle measurements by determining the optimal polynomial order to minimize residual curve discrepancies and stabilize correction data.
Implementation Method 1
Light from a light source 2 is illuminated onto angular graduations formed as slits 11 along a circumferential direction of the dial 1. Light that has passed through the slits 11 is received by a CCD linear sensor 3.
Data Source
AI summary
An angular correction method is provided for a rotary encoder in which angular skip does not occur in determining an angle at a position of switching a combination of successive angular graduation images used in interpolation calculation. An angular correction quantity Ci includes (1) a residual ri between a position computed from a model and an actually read position P, for each angular graduation image position and (2) a tangential slope f′(xi) of residual curve, r=f(x), determined by fitting the residuals to a polynomial f(x) which is a function of angular graduation image number x. The actually-read position P is corrected as P+Ci to perform interpolation calculation determining an angle without angular skip.