| Handling and processing precision products, such as Compact Discs, LCDs, LSIs and silicon wafers requires strict conditions to keep the products from acquiring tiny defects, scratches and stains. A non-contact transportation system using Near-Field Acoustic Levitation (NFAL) will satisfy these conditions. An initial experiment was firstly set up to check the validation of NFAL Phenomenon. A system consisting of an aluminum beam, two piezoelectric actuators and a mechanical horn was experimentally and theoretically analyzed. With an input of 300 Vp-p, a flat object weighing 4g could be levitated and transported with the speed up to 17 cm/s. The transportation direction can be reversed by adjusting the phase angle difference between the two actuators. Computational fluid dynamics simulation was performed to obtain the time average speed in acoustic streaming. Sliding Film Theory was then utilized to investigate the mechanism of transportation, where the shear force induced by the acoustic streaming was found to be the main source of driving the floating object. To extend the transportation, transportation over a curved path and Module-to-Module connection were experimentally performed. A beam with a shape of 90 degrees of arc was found to have uniform mode shapes and experiment results confirmed its feasibility to change transportation direction. For Module-to-Module connection, a speed threshold was discovered beyond which the transportation would be smooth without any problems. Cylinder rolling induced by the acoustic streaming was also performed to find out the dynamics of the cylinder. To optimize the system performance, the mechanical parts were analyzed in frequency domain. A close-loop system, which consists of the transportation module, vision module, and instrumentation module, was proposed. PID, Single Neuron Method and Sliding Mode Control were adopted to investigate the control effects and the performance results were mixed. |
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