A Misalignment-Tolerant High-Precision Eddy-Current Encoder for Angular Positioning

High-precision angular position sensing in robotic joints under harsh environments and strong mechanical disturbances remains a critical challenge for industrial automation. This article presents a robust, fully integrated eddy-current absolute encoder system to overcome these limitations. The system incorporates a combined single-polar and multipolar inductive coil architecture to provide high-resolution position-modulated signals. Two dedicated lock-in transceiver channels ensure real-time demodulation without switching delays, and a 32-bit microcontroller calculates the absolute angle. The effect of mechanical misalignments is analyzed, and a digital-analog collaborative dynamic calibration strategy is proposed to eliminate the resulting angular errors. This approach enables the encoder to achieve an overall accuracy of 0.0054°. By employing a least squares and error-fitting calibration method, the measured nonlinearity is reduced from ±0.1° to ±0.025°. The suppression effect of the proposed calibration method on mechanical misalignment error was experimentally verified in this article. The angular error can be reduced within ±0.035°, even with 2-mm eccentricity or 1° tilt between rotor and stator.