RESUMO
Contactless transportation systems based on near-field acoustic levitation have the benefit of compact design and easy control which are able to meet the cleanliness and precision demands required in precision manufacturing. However, the problems involved in contactless positioning and transporting cylindrical objects have not yet been addressed. This paper introduces a contactless transportation system for cylindrical objects based on grooved radiators. A groove on the concave surface of the radiator produces an asymmetrical pressure distribution which results in a thrusting force to drive the levitator horizontal movement. The pressure distribution between the levitator and the radiator is acquired by solving the Reynolds equation. The levitation and the thrusting forces are obtained by integrating the pressure and the pressure gradient over the concave surface, respectively. The predicted results of the levitation force agree well with experimental observations from the literature. Parameter studies show that the thrusting force increases and converges to a stable value as the groove depth increases. An optimal value for the groove arc length is found to maximize the thrusting force, and the thrusting force increases as the groove width, the radiator vibration amplitude, and the levitator weight increase.
RESUMO
The instability of a floating object is the main factor preventing near-field acoustic levitation (NAFL) from being widely used in the manufacture of micro-electro-mechanical systems. Therefore, investigating the restoring force due to the generation mechanisms of NAFL is necessary to ensure the stable levitation of the floating object. This study presents a theoretical analysis to evaluate the restoring force based on the gas-film-lubrication theory. The gas-film pressure between the reflector and the radiator is expressed in the form of the dimensionless Reynolds equation in a cylindrical coordinate system, which is solved by an eight-point discrete grid method due to the discontinuous gas-film distribution. An experimental rig is constructed to measure the restoring force at various eccentricities, which can be used to support the developed numerical model. The theoretical results show that the restoring force increases with an increment in eccentricity, which agrees with experimental results. Furthermore, theoretical prediction results indicate that the restoring force increases when the amplitude of the radiator and weight of the levitator increases, which indicates higher system stability. The results of the radiator vibration mode on the restoring force show that the restoring force is the largest in the first-order mode.
