Feedback and control of micro-pumps

This thesis constitutes the documentation for a Doctoral research program undertaken at the Industrial Research Institute of Swinburne University of Technology (IRIS) between 2001 and 2005. The focus of the research was an investigation of the open- and closed-loop response of piezoelectric micro-pumps for micro-fluidic applications, particularly for chemical and biomedical environments. Specifically, in order to successfully integrate micro-devices into functional systems, it was important to address issues of real-time performance monitoring and control. The research addresses some of these problems in the context of a piezoelectric-driven micro-pump, equipped with interferometric displacement feedback, which was used to measure the dynamic displacement of the micro-pump actuator surface. During the course of the research, both a discrete component and a fully integrated (laboratory-on-a-board) test system were developed for open-loop characterization of the micro-pump. The laboratory-on-a-board system was also used for closed-loop control application. Measurements showed significant differences in actuator velocity, displacement and settling time between different pumping media. In addition, transient underdamped vibration of the actuator surface was observed during the rapid excursion and recursion phases of the pump movement while pumping air. These non-contact measurements could be used to determine the open-loop characteristics of a micropump and provide information for design improvement or failure detection/analysis. The technique could also be used to provide continuous measurement for adaptive compensation, so that the pump performance criteria are always satisfied. To this end, an automated interference fringe counting algorithm was developed, so that the steadystate parameters could be mapped into the closed-loop control elements in real time. The performance of this algorithm is discussed herein, together with the implications for optimal control of the micro-pump, and eventual integration of the interferometer and micro-pump systems. The research indicated that there were potential benefits in closed-loop control of micro-pumps, particularly where failure detection was required and for pumping of non-homogeneous media. The thesis also documents the relative performance differences between open and closed-loop control in homogenous media.