Precise digital control system of a moving mirror's reciprocating move at even speed

摘要

The moving mirror's speed evenness and distance at even speed determine the spectrogram quality and resolution of the Fourier transform spectrometer (FTS). To improve the performance of FTS, a precise control system is designed to realize the moving mirror (MM)'s reciprocating move at even speed. A laser reference measurement interfer-ometer with phase-shifting through polarization is introduced, which makes the position measurement resolution reach the half wavelength of the laser. At the moment MM changes direction, the configuration of the interference signal is complicated, which induces the measurement count error using a common direction judgment method. In this paper, an improved direction judgment method is proposed based on the analysis of the interfering signal while MM changes direction, and the corresponding logical circuits are designed in Field Programmable Gate Array(FPGA). The MM is driven by a moving coil direct current (DC) linear motor, and the mathematical model is described. According to the analysis of the system characteristics and requirement, a fuzzy-PID control strategy is proposed. The fuzzy-PID control algorithm and its digital realization are studied. In order to reduce the computing quantity, the PID parameters for different inputs are calculated in advance by computer and stored in memory as tables, so the main work of the fuzzy-PID digital control algorithm is the simple look-up of the table, which makes the computing quantity very small and easy to realize in a Digital Signal Processing (DSP) chip. The control system is realized, and the experiment results show that the moving mirror's speed reaches evenness within 0.1s almost without overshoot after changing direction.