| Feasibility of utilizing MEMS technology has been investigated for a low cost, low power, and multi-line RBDS. Such a display has been previously unattainable and yet very much needed for accessing digital information. Specifically, a pneumatic display, in which elastically deformed small circular membranes emulate plurality of Braille dots, is considered. In such display, the elastic deformation of a membrane defining the tangibility of Braille dot can be controlled by a dedicated individual MEMS microvalve. On a blind subject, displays of several elastic materials have been tested. Among those, at around 4psig, 3-μm-thick polyurethane film has been identified as yielding well-defined tangible Braille dots. For such elastic material, design, fabrication, and testing of four novel electrostatic MEMS microvalves have been demonstrated.; The first microvalve, an in plane microslider, has been tested with the first- and second-generation designs in the absence of airflow, and found to suffer from design related issues. The second MEMS microvalve is an out-of-plane proof-of-concept prototype with scales relatively large for RBDS. At an applied voltage of 72.4 V-dc, the microvalve reduces the flow rate of 90 ml/min to 10 ml/min against 1.67psig. The design of the third and fourth MEMS microvalves, with scales comparable to standard Braille, has been inspired by the same out-of-plane actuation. Both valves are named after their fabrication processes as bulk- and surface-micromachined. The bulk-micromachined valve having a fairly unique structure opposes any initial air-gap and shows a zipper-like actuation against large supply pressures using relatively low voltages (72.9 V-rms for 2.8 psig and 83 sccm). Unlike the bulk-micromachined valve, the surface-micromachined valve is scaled smaller, yet uses the same actuation voltages to close against much larger pressures (68 V-rms for 12 psig and 27 sccm). Based on the theory of elasticity and gas film lubrication, steady-state coupled domain mechanical models have been developed in Matlab. Previously unknown discharge coefficients have been estimated under dimensional variations. Prediction has been made on how to build an array of surface-micromachined valves suitable for RBDS. A test has been included to compare the reading performance of blind people using RBDS to those using paper Braille. |
