Development And Application Of Control System For High-performance Powder Feeder

Laser cladding technology is a surface modification technology with great application potential,which makes the surface of the material have high hardness and wear resistance while maintaining the good tensile and torsional properties of the matrix.The powder feeder is one of the core components of the laser cladding processing system,and the quality of the cladding layer is directly affected by the performance of the powder feeder.Laser cladding processing has high performance requirements for powder feeders.In this paper,from the perspective of the control system of the rotary disk scraping and suction powder feeder,a new man-machine friendly powder feeding system is developed to solve the problems existing in the current system,such as closed-loop control lag,insufficient system integration,low power source control accuracy,and insufficient system functions.A highperformance powder feeder prototype was made and practically used in cladding processing.(1)The overall scheme of the control system was designed and the operation foundation of the control system was built.In this thesis,a powder feeder control system scheme of selfdeveloped industrial control screen+RS-485 bus communication was proposed.The scheme adopted a master-slave structure,with the industrial control screen as the master station,the servo motor and the io module as the slave station,then the master station and the slave station were connected by the bus topology.Combined with the functional requirements of the powder feeder control system software,the components required by the system were reasonably selected,the gas circuit and electrical system of the powder feeder were designed,and the operation foundation of the control system was completed.(2)The dual-barrel powder feeder control system software that can run on the arm frame industrial control screen was designed and developed in the PC,which realized the closedloop control of the motor and the monitoring of the running state of the powder feeder by the system software.According to the requirements of the bus communication protocol,the slave address,baud rate and other parameters of the slave station were configured,and the PID parameters of the servo motor were adjusted to make the motor drive the turntable to rotate stably.The coexistence of periodic message delivery and random delivery of messages might lead to bus conflicts.In order to solve this problem,a message buffer was introduced to realize the time-sharing multiplexing of the bus,and the messages can be executed in an orderly manner.In order to make full use of processor resources and arrange the program structure reasonably,the system adopted multi-threaded software architecture.On the basis of communication foundation and software architecture,various functional modules were designed and developed,and the software design and development of the entire system was completed in the PC.Using the built cross compiler,the program was cross-compiled into the executable program of the arm frame industrial control screen,and the transplantation of the system software from the PC to the industrial control screen was completed.After testing,the control system could work stably and reliably.(3)A powder feeder prototype equipped with a self-developed control system was made,and the performance of the prototype was analyzed and improved.In this thesis,a highprecision and responsive powder feeder test platform was built,and the performance of the powder feeder was tested and analyzed from three aspects of powder feeding uniformity,stability and accuracy.Continuous sampling was carried out during a single powder feeding test,and it was found that the balance indication and time were significantly linear,and the Rsquare value of the fitted line was 0.99,indicating that the powder feeding uniformity was good.The powder feeding stability was measured by the repeatability.Repeated powder feeding test was carried out under the speed closed-loop control,and the measured repeatability was±1.63%.After that,the closed-loop control function of the carrier gas flow was added in the control system.Repeated powder feeding found that when the rotating speed of the turntable was 1.0r/min,the repeatability increased to ±0.81%.The powder feeding accuracy was measured by the average deviation rate of the calibration model.Taking the powder feeding gradient test data as the calibration data,the average deviation rate of the commonly used linear fitting calibration method was 2.44%,and there are abnormal values.The average deviation rate of the fourth-order Fourier fitting calibration method was 1.05%and no outliers,indicating that the calibration method was more accurate.Analysis of the powder feeding test results shows that the powder feeder equipped with the self-developed control system has high performance and can meet the high performance requirements of laser cladding processing.Finally,thesis used the PC controller to realize the joint control of the robot,powder feeder,laser and other equipment.With the aid of auxiliary equipment such as water cooler and cladding head,the robot cladding processing system was controlled to carry out singlepass,multi-pass and multi-layer cladding experiments on 45#steel plates,and the powder feeder responded quickly.From a macro point of view,the surface of the cladding layer is smooth and has no obvious unevenness.From the macroscopic point of view,the surface of the cladding layer has no obvious unevenness;from the microscopic point of view,the dilution rate of the cladding layer is low and there is no obvious defect.From the experimental results,the robot laser cladding effect is better,the powder feeder works reliably,and the powder feeding is uniform and stable.