Abstract:
In common non-contact transportation forms such as magnetic levitation, electrostatic levitation, and gas levitation, there are problems with complex structures and control systems, as well as limited transportation materials. Ultrasonic transportation effectively solves this problem. The ultrasonic transportation structure is simple, using the acoustic field to provide support and driving force. However, due to its principle limitations, the load-bearing capacity is relatively small. Objective This paper proposed a linear transportation system that coupled acoustic field and flow field. It was supported by a 400mm long porous gas bearing and supported the heavy transported object with gas static pressure. The driving force was provided by a double-sided symmetrical ultrasonic transportation system. The ultrasonic system interacted with the transported object side to generate a traveling wave acoustic field, driving the object to move. Method The acoustic structure coupling physical field was established using acoustic theory and solved using finite element method. Based on the flow conservation equation, N-S equation, and Darcy’s law, the pressure control equation for the flow field region of porous bearings was derived and solved using finite difference method. Explored the relationship between levitation height and load capacity, and studied the effects of acoustic field gap thickness and traveling wave intensity on the magnitude of traveling wave thrust. An experimental platform for linear transportation system was built for verification. Results The experimental measurement showed that the resonant frequency of the ultrasonic system vibrating plate was 20 kHz, and the vibration mode was bending vibration. The theoretical calculation result was 20.252 kHz. The new coupled transportation system could achieve the transported object with a unit area load capacity of 1.85 kN/m
2. Under a gas supply pressure of 0.3 MPa, the object with a levitation height of 35.7 μm could be suspended, and the calculated levitation height was 38.8 μm. The error was 7.5%. The max traveling wave thrust generated when the excitation amplitude was 4 μm was 5.6 mN. Conclusion Under the same gas supply pressure, the load capacity decreased sharply with the increase of levitation height. At the same time, with the increase of permeability of porous materials, the load capacity was enhanced. As the thickness of porous materials decreased, their load capacity became stronger. The thrust exhibited periodic changes over time, with the average thrust varying with the excitation amplitude and acoustic gap thickness. The average thrust was negatively correlated with the acoustic gap thickness, and as the acoustic gap thickness increased, the average thrust weakened. The average thrust was positively correlated with the excitation amplitude, and with the excitation amplitude increased, the value of the average thrust also increased.