Research On Supporting Technique About Ultrasonic Near-field Acoustic Levitation Based On Sandwich Piezoelectric Transducer

With the development of high speed and super speed rotational machine, higher and higher requirements on bearing is needed. In order to decrease the friction resistance and enhance the shafting rotational speed to the utmost, exploitation and application of bearing with some advantages like high precise, non-contact and low friction resistance is becoming the new task in bearing field.Progress in ultrasonic technique and its combination with piezoelectric technique offer new applicable fields constantly, thereinto, piezoelectric drive technique integrating with ultrasonic vibration gains rapid growth. Researches show that ultrasonic vibration can reduce the friction between the contacting surfaces, which is obvious and benign. Moreover, the surface of sound source vibrated with ultrasonic frequency will form a strong sound field and radiation pressure, as the power is high enough, the sound radiation pressure can balance the gravity of external objects, viz. provides bearing performance, in this condition, the contacting surfaces will be separated by the air film, and it produces the suspension in ultrasonic state, which affords the foundation to the formation of ultrasonic bearing. As the ultrasonic suspension bearing brings forward, a new research direction on bearing is started, which makes the expansion and appliance on piezoelectric drive technique multiple. The new noncontact suspension bearing is still in the basic research period nowadays, so the exploration is necessary.In this paper, combined with the national natural science fund—the support technic research on ultrasonic suspension of flywheel energy storage system high speed shafting, and suspending effect in the sandwich piezoelectric transducer and ultrasonic vibration provides the foundation, suspension bearing shafting is constructed, and research on sound suspending technic under ultrasonic vibration is taken on completely and by the numbers, which is novel and establishes foundation to the subsequent research. The research in the paper involves piezoelectricity, ultrasonics, vibration analysis and mechanics and so on. The paper includes the following five aspects.1. The development and appliance on suspension bearing techniqueThe development state of suspending bearing technique home and aboard, together with its appliance in mechanical field are discussed in this paper. To construct suspension bearing, the traditional implement includes magnetic suspending technique and gas static pressure suspending technique, and they are similar to some extent with ultrasonic suspension technique here, which can realize the noncontact working state between rotor and bearing, and minish friction and increase the shafting rotate speed. The forming theory, performance and appliance characteristic of magnetic suspension and static pressure suspension is analyzed mainly in this paper. Ultrasonic vibration reducing friction and suspending technique is set forth. The ultrasonic vibration reducing friction can be the comparing subject with ultrasonic suspending technique, and can provide valuable reference for research.2. Theoretical analysis and discussion about acoustic levitationThe relative theory of ultrasonic suspension is discussed in this paper, which provides theory gist and technique support for the design of sandwich piezoelectric transducer and suspending supporting system, and this discussion does great directing roles to design reasonable construct of near source sound suspension supporting system, to do deep research on suspension supporting technique, and to realize ultrasonic suspension technique appliance in bearing field.The basic issues like the spread of ultrasonic vibration; the formation of sound radiation pressure is studied. Based on the theory such as gas lubrication and extrusion gas film, effect mechanism on ultrasonic vibration and suspension is explained; the mathematical model of sandwich piezoelectric transducer is founded, and theory research on near source suspension performance is carried on.Experimental research on minishing friction performance and suspension bearing capacity of sandwich piezoelectric transducer during portrait ultrasonic resonance state is carried through. In this foundation, based on sandwich piezoelectric transducer sound suspension, the construction of ultrasonic suspension supporting system is feasible.3. The design of sandwich piezoelectric transducerSandwich piezoelectric transducer is the critical element to construct ultrasonic bearing system, and is one of the emphases of the suspension supporting technique research. Construction and performance of sandwich piezoelectric transducer is taken apart, and its working principle is clarified, the facture process of piezoelectric transducer is discussed, a good many working performance factors of piezoelectric transducer is analyzed completely, and provides evidence for design and construction.Combined with suspension supporting technique research, the concrete configuration and size parameter of sandwich piezoelectric transducer is designed. A number of frame style sandwich piezoelectric transducer such as plane, taper and concave cylinder in the vibration output end is opened out. The mathematical model of transducer is established. The sound suspending performance of transducer with special configuration is analyzed. Vibration mode of piezoelectric transducer is analyzed with FEM. Its impedance, phase angle, syntony frequency and so on are tested by precise impedance analyzer, and the essential performance parameter of transducer is obtained. In the foundation, the configuration of the transducer is optimized.4. Design and proto type trial-produce of ultrasonic near-field acoustic levitation supporting systemIn order to make design of the ultrasonic bearing system reasonable, to the basic requirement of shafting system design, some basic issues of shafting design period is considered, the design idea of near source sound suspension supporting system is bring forward, under the direction of design idea, the design and proto type trial-produce of suspension supporting system is put up.In the foundation of sound suspension theoretical analysis and sandwich piezoelectric transducer configuration design, design of ultrasonic suspension supporting system with many special configuration types such as thrust bearing, concave cylinder radial supporting bearing and bidirectional angle supporting bearing is finished.7 experimental proto types are trial produced. Design purpose of every kind of suspension supporting system is clarified, the configuration design process is expanded. And shafting supporting, orientation and driving mode is discussed mainly, at the same time, configuration characteristic of every proto type is analyzed from the technique research view.Design and trial produce of suspension supporting system proto type founds a basement for the experimental research on suspension supporting technique.5. Experimental research on ultrasonic suspension supporting system based on sandwich piezoelectric transducerExperimental research on ultrasonic suspension supporting system is the hard core in the paper, the content includes:1. Experimental research on sandwich piezoelectric transducer with plane surface, taper surface and concave cylinder surface ending configuration is carried through. In some condition, the displacement amplitude of the vibration end is tested, suspension bearing capacity of sandwich piezoelectric transducer during portrait syntony state is tested, the transformation course and trend of the suspension gap between transducer vibration output end and external load is described objectively. The relationship of bearing capacity with suspension gap, vibration frequency and input voltage and so on is established, and the curve is protracted. 2. Ultrasonic trust bearing testing system based on plane surface end sandwich piezoelectric transducer, double vibrators radial and axial supporting ultrasonic suspension bearing testing system based on plane surface and concave cylinder surface end sandwich piezoelectric transducer, and double vibrator angle supporting ultrasonic suspension bearing testing system based on taper surface end sandwich piezoelectric transducer are researched through experiment. To the three representative ultrasonic suspension supporting system design and fabricated in this paper, bearing capacity, utmost rotate speed, dynamic friction torque and so on are tested respectively. The suspension supporting state and factors influencing the suspension bearing working capacity is analyzed thoroughly. Through a number of experimental researches, the configuration design of the suspension bearing system is proved to be rational and feasible.3. In order to improve the working performance of piezoelectric transducer, enhance the energy transition efficiency of piezoelectric transducer and the systemic stability during work period, multiple match styles is adopted, experimental research of sandwich piezoelectric transducer resistance suit is carried through.