Abstract
Microfluidics, a field to deal with a small amount of fluid using a chip which had a lot of micro-scale channels, has applied in various fields including biology, chemistry, biomedical, and cell biology for recent few decades. One of the sub-categories of microfluidics is a droplet generation. A syringe pump is usually employed as an injection system. However, the injection system has some problems such as overshoot, steady-state error, and response delay. This paper grasped the problems of the conventional syringe pump, and then proposed a robust control method to control the flow rate precisely. Since the syringe pump includes parametric uncertainties in the system mainly due to the variation of the ball screw friction and the elasticity of the rubber, the robust control mechanism was designed with the cascade structure composed of the inner loop (i.e. disturbance observer and sliding mode control) and the outer loop (i.e. flow rate disturbance observer and 2-DOF control) against the undesired adverse effects. Finally, the proposed control scheme is evaluated through the experiment for its robustness and performance.
Highlights
Microfluidics is the research to deal with a small amount of fluid using a chip which had lots of microscale channels [1]
Under the precise velocity control, flow rate disturbance observer (FOB) is used to make the syringe pump system more robust against the nonlinearity of friction coming from the ball screw and the rubber
While sliding mode control (SMC) works to improve tracking performance and to guarantee the robustness of the proposed control method resisting to the high-frequency components of the lumped disturbance, disturbance observer (DOB) makes the mechanical part behave as a defined nominal model against model uncertainties and disturbances in lowfrequency range [25], [26]
Summary
Microfluidics is the research to deal with a small amount of fluid using a chip which had lots of microscale channels [1]. Where Fd is the unexpected external disturbances, Ff is the friction force owing to the elasticity of rubber in the syringe, M is the equivalent mass of the mechanical system, C is the equivalent friction coefficient from the high rate reduction gear and the ball screw as driving part. The response of the mechanical system varies in low-frequency region with respect to input torque commands This phenomenon is occurred due to the model uncertainty mainly caused by the cyclic variation and the friction of the ball screw. In order to design the robust and precise controller for the mechanical system, the transfer function from the motor torque to the velocity of the piston is obtained as follows
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