Modeling And Control Of High-power White LED Micro-coating Process

With the development of the lighting industry,efficient and environmentally friendly high-power white LED light sources have become a new hot research direction.Coating technology is an important part of the LED packaging process.Whether the phosphor powder coating is uniform or not directly affects the LED's luminous effect.However,in the actual coating process,because the coating thickness,shape,and position cannot be accurately controlled,the coating surface is too thin or too thick,and the coating area often misses or overflows,which eventually lead to inconsistent light output effects.Therefore,it is very important for the coating process to model and control.The coating process involves multiple links,and phosphor powder is non-Newtonian fluid,which has complex rheological properties and strong non-linear dynamic characteristics.It is currently difficult to establish a general and accurate process control model.Achieving stable uniform coating has become an urgent problem to be overcome in the LED packaging process.Therefore,this article studies the precise coating problem in the LED packaging process from the perspective of modeling and control,main tasks as follows:(1)Overview of key technologies in the coating process.This paper introduces the research background,and explains the key technologies such as coating methods,process modeling and control involved in the coating process.(2)Analysis of coating process.Starting from the characteristics of the coating system and coating materials,the rheological properties of phosphor glue and related factors that affect the coating thickness and uniformity are analyzed to provide a theoretical basis for modeling and control of the subsequent coating process.(3)Research on fluid modeling and numerical simulation.Modeling and analyzing the flow of typical fluid in the atomizing nozzle tube with simplified motion and finite element method,and performing numerical simulation by using computational fluid dynamics technology.The analysis focuses on the influence of nozzle inner diameter and length,atomizing pressure,and feed pressure on the fluid flow rate.(4)Experimental modeling of coating thickness.Firstly,with predicting the coating thickness and improving the uniformity as the target,the effects of variables such as atomizing air pressure,feed air pressure,and coating time were studied.Secondly,regression analysis and neural network analysis were used for modeling.Then,verifying and comparing the prediction accuracy of the two modeling methods.Finally,based on the measured thickness and related assumptions,the coating amount estimation formula is derived to provide the basis for parameter adjustment and control for the phosphor coating process.(5)Process control of coating system.Because the complex model form is difficult to be used directly to design the controller,considering the influence of environmental factors,this article divides the atomization coating control process into two steps: first,the colloid viscosity is tracked and controlled steadily,and then designing the compensation control system for the coating amount,by adjusting the key parameters of the system to improve the coating effect.