Innovative Method for Measuring the Dynamic Pump Chamber Pressure inside a Micro Diaphragm Pump
The transport of fluid is an essential task in a variety of applications like air quality monitoring, or medical applications such as hydraulic implants and drug delivery. In any of these, smaller and more energy efficient dosing units are of advantage. However, especially medical applications pose demanding requirements in terms of safety, reliability and size. To this end, miniaturization of fluidic components, such as micropumps is an ongoing field of research. An example of a system where a micropump would be beneficial is the urinal sphincter implant, where state of the art is the use of a manual pump or an electric pump with substantially larger dimensions to generate enough pressure in order to pinch off the urethra with an inflatable cuff. Another example are microfluidic drug delivery systems, which need micropumps to reliably and accurately administer the right amount of medication to the patient. Micropumps are a key component to improve these applications. The Fraunhofer EMFT has a micropump platform that can be adapted to meet the requirements of specific applications. To enable targeted adaptations, the fluidic properties of a pump design can be predicted with lumped element models. However, a model is just a projection of reality though and needs to be verified by empirical measurements. Some predictions like the volumetric flow rate and pressure capability can be validated with measurements but a more sophisticated approach is necessary to verify the assumption that the pump chamber pressure is constant throughout the micropump. This work provides a tool for the Fraunhofer EMFT, which gives insight into the micro diaphragm pump during operation, in order to validate and improve current models. To this end, an innovative method to measure the dynamic pump chamber pressure inside of a micro diaphragm pump is introduced. The Fraunhofer EMFT micropump design is adapted to house several diaphragms in order measure their deflection and correlate them to a pressure. Two different designs are manufactured: one design to investigate the radial dependency of pressure in the micropump in order to improve the dimension of the chamber radius; a second design to measure the pressure at the inlet and outlet valve, to find the ideal distance between them. The manufacturing is split in two batches with 32 micropumps overall. The micropumps consist of several thin metal foils and a thicker main body which are laser welded together. During the first batch, challenges in the manufacturing process occurred, since the thermal input of the laser causes bulges on the thin sensing foil resulting in non-airtight welding seams. Shifting the sequence of the metal foils helped as a countermeasure. The micropumps of the second batch are tested with a measurement setup that is built to measure the deflection of the pressure sensing diaphragms during the operation of the micropump. A quasi static calibration measurement allows to correlate the detected deflection to a pressure in the pump chamber. The calibration measurements reveal a linear dependence between pressure and deflection which is predicted by analytical calculations for low deflections. Dynamic mea surements of the samples indicate a superimposition of the pressure signal and the piezoelectric actuator movement of the micropumps. Comprehensive failure analysis leads to the conclusion that the distortions result from the micropump moving. Soft rubber sealings between the housing and the micropump allow movement, as well as the 3-D printed holder that holds the micropump housing in place during measurements. The first distortion is eliminated by gluing the micropump into the housing, while the second distortion has to be removed by a more sturdy holder or an additional distance sensor. The knowledge gained from this approach contributes to the expertise on micropumps and thus enables microfluidic systems with micropumps to become reality in various applications in the future.
München, TU, Masterarbeit , 2022