A Novel Technique of Phase-locked Interference Positioning and Phase Discrimination

摘要

A novel ultra-precision positioning technique based on phase tracking and locking is presented, which extremely simplifies the structure of the ultra-precision positioning system by taking the phase difference between the measuring signal and reference signal of dual-frequency laser interferometer instead of monitoring displacement data from interferometer as the control signal of micro-displacement actuator. In order to real-time compensate static positioning errors of the system due to factors such as hysteresis and creeping of the working platform, the phase discrimination unit must meet requirements on high frequency response and high precision. To avoid the shortcomings such as low phase discrimination accuracy and narrow measuring bandwidth of the conventional analog and digital phase difference detecting methods, an integrated circuit used in communications for phase difference detecting, AD8302, is introduced into the ultra-precision measuring and control circuit, and a high precision phase discrimination circuit with a measuring bandwidth covering 20kHz to 80MHz is developed after thorough study of the principles of XOR-type phase discrimination, and phase shifting method is used to solve the polarity problem brought by direction discrimination. Experiment results show that the accuracy of phase discrimination is better than 0.1° within the phase difference range of -180° to +180° at the center frequency 20MHz, and the corresponding displacement resolution of the positioning platform is 0.05nm. This technique can also be applied to the phase discrimination units of other instruments and equipments.