Design of Position Error Compensation Based on MCU and FPGA for High-Precision Quadrature Encoders

초록

This study proposes a digital pulse-level compensation method for correcting pre-characterized position errors in systems that employ incremental encoders. Encoder resolution in existing systems is often enhanced through interpolation rather than relying solely on native resolution. However, interpolation and signal conditioning can be affected by electrical noise, mechanical vibration, interpolation distortion, and signal-conditioning errors, which may lead to erroneous position feedback. To address this issue, the proposed method performs pulse addition or removal at predefined encoder-count positions identified through offline calibration. Experiments were conducted using the Encoder Pulse Compensation Board (EPCB) integrated into a Laser-Cutting Robot. For verification, the laser-cutting process was carried out by moving the servo motor 100 mm along the X-axis. With the proposed digital pulse adjustment applied, the pre-characterized missing and redundant pulse events were successfully compensated. Consequently, the machined holes exhibited diameters between 195μ m and 203μ m (mean: 200μ m), with deviations remaining within -2.5% and + 1.5% across 100 consecutive trials. These results confirm that the FPGA-based logic executes deterministic pulse correction with low latency, enabling consistent high-accuracy cutting under the tested conditions. Notably, the FPGA embedded in the EPCB enables parallel processing of encoder signal acquisition and filtering logic. The proposed FPGA-based design reduced the combined encoder signal acquisition and filtering latency by 45.3% (from 267μ s to 146μ s) compared to the sequential input processing used in the MCU-only method. Furthermore, the 16-bit parallel I/O interface between the FPGA and the MCU enabled real-time data communication, allowing for the high-speed transmission and reception of large data volumes. Thus, the algorithm shows potential for use in a wide range of applications requiring position feedback for precise control. © 2013 IEEE.

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