Development of a robust closed loop pressure control system for droplet generation

In droplet microfluidics, the precision of droplet length is essential for assay consistency. Pneumatic control is commonly utilized to regulate fluid flow and droplet generation, but the absence of feedback in open-loop systems makes these systems vulnerable to disturbances and restricts dynamic pressure regulation. To minimize variability and optimize resilience to perturbations, a closed-loop control strategy was implemented with the help of a proportional valve regulating the pressure in a sealed container. Using system identification, a mathematical model for the pneumatic system was developed to form the basis for a closed-loop Proportional-Integral (PI) controller. Compared to conventional methods, that derive mathematical models using physical laws, system identification is used to simplify complex models and design an effective robust controller while considering experimental uncertainties. The effectiveness of the closed-loop feedback system was evaluated for dynamic pressure changes and disturbance rejection. This resulted in a significant reduction of the coefficient of variation (CV) from 9.32 % (best-case scenario) during open loop control to < 3 % during closed loop control. Additionally, the stability of container pressures over a 30-minute period demonstrated a 25-fold improvement compared to open loop, alongside 1.6-fold enhancement in stability in droplet length.