Research Of Automatic Control Method Of Wavelength Tunable Laser For Laser Raman Spectrograph

With the advantages of rapid detection and high accuracy,laser Raman spectroscopy has become the main mean to study the molecular structure.And it is widely used in chemical catalysis,biological macromolecule,environmental detection and other fields.However,the grating of wavelength-tuned laser in laser Raman spectrometer is segmentally controlled and laser wavelength could not be continuously adjusted online in frequency-doubling system.Therefore,it is of great theoretical and practical significance to realize automatic control of gratings and mirrors in frequency-doubling system by means of motors and computer control system so as to realize continuous adjustment of laser wavelength on line.This paper introduces the whole design scheme of the automatic control system of the ultra-violet-visible laser of Raman spectrometer.The system mainly consists of the power-supply module,motor drive control module,and human-computer interaction module.The motor drive control module is the core of the system,which consists of motor driver module,multi motor synchronization and reset module,motor measurement module and data communication module.In the hardware control platform,the micro controller MC9S12XS128 of Freescale is chosen as control core.And the software control platform is based on the CodeWarrior5.0 software.With Lab Windows/CVI software platform,display monitor interface is designed which can real-time display the running states of the control system,the speed and angle of each motor,and set the initial value and parameter control range of the control system.This paper makes a detailed introduction on the operation principle and mathematical model of brushless DC motor.In order to overcome the problem that BP neural network is easy to fall into local optimum,the particle swarm optimization with nonlinear inertia weight factor is introduced to optimize BP neural network.The algorithm is used to control the brushless DC motor speed regulation system and the simulation platform is built in the MATLAB/Simulink environment.Simulation results show that the brushless DC motor control system based on improved PSO-BP neural network has better dynamic and static response,and also shows strong resistance to external disturbance.The speed control system has better stability,stronger adaptability and robustness.