Hysteresis Switch Adaptive Velocity Evaluation and High-Resolution Position Subdivision Detection Based on FPGA

The high-performance measurement of velocity and position is an important requirement for applications of motion control and servo drive. This paper presents a new methodology to derive the velocity and position information by processing the pulses from an optical incremental encoder. Compared with the conventional adaptive method, the proposed velocity evaluation method adopts the hysteresis switch technique to remove the switching fluctuation. Further, a time-to-digital converter performed with phase-locked loop is used for accurate time interval measurement, consequently, improving the resolution of velocity evaluation. In addition, to achieve higher accuracy of position detection, the calculated velocity and subdividing position are employed to compute the position. The measurement system is implemented in the field-programmable gate array, which consists of five blocks: 1) clock frequency multiplier; 2) pulse decoder; 3) velocity evaluation unit; 4) position detection unit; and 5) Nios II CPU. The theoretical analysis and experimental results validate the proposed velocity and the position measurement method outperforms the present methods.