Research Of Droplet Microfluidics Control System Based On Stepper Motor Microvalve

Droplet microfluidic technology has a wide range of applications in the fields of biomedicine,chemical engineering and other fields.At present,droplet generation devices are mostly based on conventional size control elements,such as pneumatic proportional valves,syringe pumps,etc,which expands the volume of droplet microfluidic systems,narrows its scope of application.For this reason,the droplet microfluidic system based on stepper motor microvalve is proposed in this paper.Microvalve is used in place of the conventional valve group.It has the characteristics of miniaturization and is easy to integrate with other microfluidic components and can be used to generate stable size fluids.The droplet microfluidic system solution of the stepper motor microvalve proposed in this paper realizes the droplet size adjustment function by controlling the liquid driving pressure.A dynamic mathematical model of the droplet microfluidic system was established.The spool displacement equation of the microvalve of the stepper motor,the microvalve flow rate equation and the force balance equation of the valve membrane were deduced;the droplets in the T-junction microchannel were deduced.The static/dynamic dimensional change was deduced,and the liquid pressure resistance model was used to analyze the pressure-flow relationship in the T-junction microchannel and the pressure-driven droplet size formula was obtained.The static and dynamic characteristics of the stepper motor microvalve and the open-loop characteristics of the pressure control system were simulated and analyzed using Matlab/Simulink,finite element software Fluent,and Comsol.The motion characteristics of the stepper motor microvalve were obtained.Microvalve static flow characteristics.The equivalent flow resistance model of the system is proposed,and the transfer function of the system is obtained by using the linearization theory.The difference between the single valve and double valve control is compared and analyzed;the micro-valve flow path size,pressure volume,and other parameters to the effect of open loop characteristics are analyzed.At the same time,the conditions of droplet generation under pressure drive are analyzed.The dimensional stability of droplets is analyzed and the method to improve the droplet size stability is proposed.In this paper,according to the open-loop characteristics of the system,the control algorithms such as PID and Bang-Bang are designed to perform closed-loop control of the system.The effects of the two methods are compared through simulation.The single-valve and double-valve control strategies for pressure control are proposed and compared.An optimal solution for pressure control is proposed.The droplet microfluidic system experimental platform is established,and the processing methods for the important components of the system are designed and manufactured,such as the production of microvalve chip and T-junction microchannel chip,and the points of attention in the actual operation are given.The droplet microfluidic system in this paper can achieve two-channel pressure control,which are independent of each other and can be used alone or in combination for droplet generation.Based on the experimental platform,different pressure control algorithms were tested and compared,and the actual effects of the single valve and double valve control were tested and used for droplet generation experiments according to their performance.This paper describes the experimental preparation and experimental flow of droplet generation,analyzes the process of droplet generation under pressure drive,measures the droplet size variation under pressure step response,and proposes a droplet size calculation method based on image processing which realizes the real-time monitoring of droplet size.