Design And Implementation Of Self-Focusing Module Of LIBS Remote Detection System

In recent years,with the rapid development of Chinese industry,the soil heavy metal problem is increasingly prominent,which has caused great harm to human health,economic development and natural environment.However,the existing soil detection system has poor timeliness and huge resource consumption.In order to timely detect some heavy metal pollution events and carry out soil control work smoothly,it is very necessary to establish a set of real-time,online and fast intelligent monitoring system for heavy metal pollution in soil.In this monitoring system,in order to realize real-time on-line detection and reduce the consumption of human and material resources,remote detection method is adopted.Laser induced breakdown spectroscopy(LIBS)has been widely used in the field of soil detection because it can be in situ,remote,and multi-element joint measurement.In this paper,a self-focusing LIBS system is designed based on the principle of LIBS remote detection to meet the requirements of soil heavy metal detection,including the design and development of hardware control,optical structure and self-focusing motion control program.Then,the performance of the self-focusing structure is verified according to the results of quantitative analysis of soil Cr element.Mainly carried out the following work:(1)Taking zoom optical system as the main body,complete the mechanical integrated design of laser,laser rangefinder,servo motor,electronic ruler,spectrometer,raspberry PI and power supply and other equipment,and complete the overall control circuit and communication connection design of integrated equipment.(2)Based on the Cassegrin-Schmidt telescope,the self-focusing structure of the LIBS remote detection system is designed and built.This structure is a zooming optical structure with laser focusing and signal light collection coaxial,and the energy threshold limit,working efficiency,spherical aberration,chromatic aberration and other parameters of the entire optical system are optimized,which makes the plasma imaging quality better.And the energy loss rate is 35%.(3)Using Raspberry PI as the main control system,serial communication as the basis,based on RS485 data transmission protocol,through Python language to complete the development of self-focusing motion control program,zoom distance of 1～5m,zoom accuracy can reach 1cm.The program can realize the zoom by changing the position of the secondary mirror in the self-focusing structure.During the auto-focusing process,the secondary mirror can be divided into two motion modes,high power and low power.The movement error is less than 100μm,and the zoom response time is less than 2s.(4)The preliminary test of the equipment was completed.According to the test results,the optimal working distance of the equipment combined with the UAV was 2～4 meters.The soil Cr content was measured through automatic focusing,which verified the accuracy and stability of the equipment detection.