Abstract
The measurement results of a single-excitation petal-shaped capacitive encoder show strong periodic characteristics for nonlinear errors. This paper presents the analysis of periodic nonlinear errors in a single-excitation petal-shaped encoder in terms of three main aspects—sensitive structure processing error, circuit demodulation error, and installation error. Analytical and simulation results confirm that the first-, second-, and fourth-periodic electrical errors are caused by the misalignment of circuit parameters, non-uniform segmentation of the processing error, and cross interference of the electric field, respectively. Further experimental investigation reveals that the mechanical periodic error is caused by installation misalignment. Based on these analytical, simulation, and experimental results, the design of the capacitive encoder was optimized and a method based on harmonic components was applied to compensate the periodic nonlinear error of the encoder. Measurement results shows that the prototype which has 180 petal-shaped numbers can achieve a reduction of periodic nonlinear errors to less than 0.02° and its accuracy can be improved to 0.0006° after compensation over the full measurement range.
Highlights
Rotary encoders are widely used to provide positional feedback information and achieve precise control [1,2,3,4,5]
To further improve measurement accuracy of the petal-shaped capacitive rotary encoder, This paper focused on three aspects of the single-excited petal-shaped capacitive encoder—its sensitive structure processing, demodulation circuit, and installation error—to distinguish the contribution to the periodic nonlinear error
This study,the the of of a of single-excited petal-shaped capacitive rotaryrotary encoder In In this study, nonlinear error errorsources sources a single-excited petal-shaped capacitive encoder were theoretically analyzed, with the results showing that the nonlinear sensing error has were theoretically analyzed, with thewith results the nonlinear error has good periodic encoder were theoretically analyzed, theshowing results that showing that the sensing nonlinear sensing error has good periodic characteristics
Summary
Rotary encoders are widely used to provide positional feedback information and achieve precise control [1,2,3,4,5]. Many types of capacitive encoders have been proposed, and the most prominent is by modulating the angular information to two orthogonal triangular signals [6,7,8] Encoders of This type have the advantage of high robustness to common mode errors. [13], a single-excited petal-shaped capacitive rotary encoder was proposed and achieved a measurement accuracy of 0.008◦ , but periodic nonlinear error exists and the analysis of the encoder is insufficient. The repeatability and periodicity of the nonlinear error results reported in Ref. To further improve measurement accuracy of the petal-shaped capacitive rotary encoder, This paper focused on three aspects of the single-excited petal-shaped capacitive encoder—its sensitive structure processing, demodulation circuit, and installation error—to distinguish the contribution to the periodic nonlinear error.
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