Precise and robust position estimation for optical incremental encoders using a linearization technique

• An amplitude-to-phase converter incorporating linearization technique is proposed.
• Theoretical error of the converter is within ±0.0196 μm for 20 μm optical encoder.
• The converter is more robust than the commonly-used arctangent method.
• Signal phase-shift error has a large influence on the positioning accuracy.
• A circuit is developed to convert phase-shift error to amplitude imbalance error.

In this paper, an amplitude-to-phase converter for optical incremental encoders is presented. The proposed converter is based on a linearization technique that coverts the sinusoidal signals into a nearly perfectly linear output signal, from which displacement can be determined precisely using a simple linear equation. The theoretical error of the converter is within ±0.0196 μm for an optical encoder with a period of 20 μm. Simulation results indicate that the proposed converter is significantly more robust to the signal imperfections than the commonly used arctangent algorithm. A signal pre-processing circuit is also developed to further reduce the positioning error caused by the signal phase-shift error. The proposed converter was successfully implemented with a Field Programmable Gate Array (FPGA), and applied to an optical encoder. The robustness and effectiveness of the converter have also been confirmed from experimental results.