Research On Automated Sample Exchange System For General Purpose Powder Diffractometer

China Spallation Neutron Source(CSNS)is located in Dongguan,Guangdong Province,which is the key construction of major scientific research infrastructure in China.Upon its completion,China will become the first developing country in the world to have spallation neutron source.General Purpose Powder Diffractometer(GPPD)is one of the first three diffractometers built by CSNS.Its high energy resolution and suitable neutron flux provide different experimental conditions to meet the requirements of most scientific researchers using powder diffraction diffractometer to study the material's crystal structure and magnetic structure.In order to improve the efficiency of neutron powder diffraction experiments,the automation technology needs to be applied to the sample changing system.In this paper,according to the changing needs and structural features of GPPD,we designed an automated sample exchange system which can accurately grab and place the sample,automatically grab the sample into the neutron beam in sequence,and adjust the position of the sample which is the strongest at the beam.The system can achieve the continuous experimental operation of multiple samples in one installation without destroying the vacuum environment.The main contents of this paper are as follows:In chapter 1,the development of domestic and foreign spallation neutron source and the status quo of the General Purpose Powder Diffractometer of the China Spallation Neutron Source are summarized.The foreign research status of automated sample exchange system of neutron diffractometer is introduced.The main research content and significance of this paper are proposed.In chapter 2,based on the functional requirements and performance requirements of the automated sample exchange system,the overall system is designed.The designed automated sample exchange system includes sample moving structure,sample changing structure,sample grabbing structure,vacuum structure and monitoring device,etc.The match of the servo motor and load on torque and rotary inertia are analyzed.In chapter 3,by analyzing the static stiffness model of the ball screw feed system of the automated sample exchange system,the dynamic model of the feed system is established.The model is more similar to the real physical model than traditional ones by taking the stiffness of the feed system changing with the change of position and the nonlinear friction into consideration.Simulink software is used to simulate the model,and the dynamic response of the feed system is obtained.In chapter 4,a PLC-based servo motor drive system is designed.This system has two control modes:remote and local,and the remote control mode is divided into automatic mode and manual mode.EPICS-based human-computer interaction system has been developed to provide users with a simple and intuitive user interface and to communicate with the PLC through DB files.In chapter 5,the assembly of the automated sample exchange system is introduced.The response characteristics of the system in the time domain and the frequency domain are experimentally studied.The performance parameters of the system such as response speed and motion stability are analyzed in detail.In chapter 6,the summary of the whole work and the prospect in the future are proposed.