Search

In this article, to achieve high torque density and high power density of rotary ultrasonic motors (USMs), we develop a rod-shaped transducer operating in torsional/bending (T/B) modes and excite two elliptical motions on its bilateral ends to drive the rotor orthogonally pressed onto the transducer. Here, the torsional vibration, the driving structure, and the rod shape may enable the T/B motor to provide high driving force, large driving distance, and low weight, which facilitate the realization of high torque density and high power density. To assess the validity, first, we construct a transducer 43 and 110 mm in diameter and length, respectively. Then, we investigate the load characteristics of the T/B motor: When it works at the frequency of 21.64 kHz, the maximal torque and the maximal output power reach 10.1 N·m and 38.1 W, respectively. In the meantime, it yields the torque density and the power density of, respectively, 20.0 N·m/kg and 75.7 W/kg, which are, as predicted, relatively high compared to the values of most conventional rotary motors. This article not only validates the effectiveness of our proposal but also provides a new approach to design powerful rotary USMs.

Our previous studies showed that traveling-wave rotary ultrasonic motors with polymer-based vibrators yielded limited output power when operating in the commonly used low-order bending vibration modes. In this study, we employ a high-order bending mode in the polymer-based cylindrical ultrasonic motor, because this mode yields a relatively high electromechanical coupling factor, which may lead to high output power of the motor. Additionally, in contrast with the low-order modes with only vertical nodal lines, the high-order mode has both horizontal and vertical nodal lines on the circumferential outer surface of the polymer-based vibrator. With these attractive advantages, it is worth investigating basic vibration characteristics of polymer-based vibrators operating in high-order modes and their applications to ultrasonic motors. The vibrating body is made of poly phenylene sulfide, a functional polymer exhibiting low mechanical loss even under high-amplitude ultrasonic vibration and is activated by a piezoelectric ceramic element bonded on the back surface. The high-order modes are optimal for polymer-based vibrators with practical thicknesses, because their equivalent stiffnesses and masses are relatively low when operating in this mode. Polymer-based motors with the high-order modes exhibit relatively high output torques and powers, compared with not only polymer-based motors with low-order bending modes, but also metal-based motors operating in high-order vibration modes.

With their characteristics of low density and elastic moduli, polymers are promising materials for making ultrasonic motors (USMs) with high energy density. Although it has been believed for a long time that polymers are too lossy to be applied to high-amplitude vibrators, there are several new polymers that exhibit excellent vibration characteristics. First, we measure the damping coefficients of some functional polymers to explore the applicability of polymers as vibrators for USMs. Second, to investigate the vibration characteristics, we fabricate bimorph vibrators using several kinds of polymers that have low attenuation. Third, a bending mode USM is fabricated with a polymer rod and four piezoelectric plates bonded on the rod as a typical example of a USM. Through an experimental investigation of the motor performance, it was found that the polymer-based USMs exhibited higher rotation velocity than the aluminum-based USM under a light preload, although the maximum torque of the polymer-based USMs was smaller than the aluminum-based USM. Among the tested polymers, polyphenylenesulfide was a prospective material for USMs under light preloads because of the high amplitude and lightweight of polyphenylenesulfide.

If an ultrasonically vibrating pipe is dipped into a liquid, the liquid is pumped up inside the pipe. We found in a previous study that the maximum pressure was improved from 1 kPa to 7.2 kPa if the end of the pipe was installed on a plate with a small gap. In this study, the configuration is modified for a practical design in which a still pipe is located at a right angle to a piston-vibrated surface. We investigate the difference in the pump characteristics between the former and new configurations. Our experiments show that a maximum pressure of 20.6 kPa is obtained by optimizing the inner and outer diameters of the pipe as well as the gap between the pipe end and the vibrator.

The sound intensity vector provides useful information on the state of an ultrasonic field in water, since sound intensity is a vector quantity expressing the direction and magnitude of the sound field. In the previous studies on sound intensity measurement in water, conventional piezoelectric sensors and metal cables were used, and the transmission distance was limited. A new configuration of a sound intensity probe suitable for ultrasonic measurement in water is proposed and constructed for trial in this study. The probe consists of light-emitting diodes and piezoelectric elements, and the output signals are transmitted through fiber optic cables as intensity-modulated light. Sound intensity measurements of a 26 kHz ultrasonic field in water are demonstrated. The difference in the intensity vector state between the water tank with and without sound-absorbing material on its walls was successfully observed.

With the properties of low density, low elastic modulus, and low mechanical loss, poly(phenylene sulfide) (PPS) is a suitable material as the elastomer in an airborne ultrasonic transducer for generating large vibration velocity. In this study, we design and fabricate a transducer composed of a PPS-based longitudinal vibrator and a PPS-based disk of 0.3 mm thickness to obtain high-intensity ultrasound. The rated sound pressure at a distance of 300 mm reached 38.9 Pa (125 dB, 0 dB re. 0.02 mPa) when the frequency and voltage were 58.90 kHz and 20 V. The weight of this transducer is 6.3 g. The ratio of the sound pressure to the weight of the prototype transducer is 1.8 times larger than that of the commercial transducer. The experimental results indicate that PPS is a good substitute for metal as the elastomer for manufacturing airborne ultrasonic transducers with a high output-to-weight ratio.

A 1.8 cc silent bidirectional traveling-wave, self-moving linear microactuator is shown to be capable of generating a sliding velocity of 0.22 m/s and sliding force of 1.1 N. Through the use of computational analysis in the actuator's design, the vibration characteristics were improved in order to obtain a better actuator. The generation of a radial traveling wave about the circumference of the actuator, akin to a ring, is shown to exist despite the unusual shape, and the presence of traveling wave motion along the output face also is shown to exist. By using short-time sinusoidal signals, slider displacements as small as 82 nm were obtained from the actuator, and by using direct current (DC) input, displacements of up to /spl plusmn/107 nm were obtained, suggesting a way to obtain subnanometer positioning accuracy over arbitrary sliding distances. By reversing the phase between the paired driving signals, the direction of motion was reversed at up to 300 Hz; the slider displacement and velocity was found to be inversely proportional to the phase-reversal rate, and the slider's peak velocity and maximum thrust force were directly proportional to the phase between the driving signals. The output force and velocity of the actuator was fairly insensitive to the input frequency, giving measurable motion between 132.5 and 141.5 kHz, but was sensitive to the input voltage, requiring at least 38 V input for operation, and was approximately quadratically dependent on the applied preload centered about 2.25 N.

A torsional microtransducer for high-power applications was developed using standard bulk lead zirconium titanate (PZT) placed upon a small rectangular prism made from phosphor bronze, with a tapered conical end serving as a horn and a machined interior to improve the actuator's response. Torsion was obtained from a prototype at the design frequency of 192 kHz as well as over a wide range of frequencies from 136 kHz to 1.02 MHz. Torsional vibration velocities of 335 mm/s at 192 kHz were measured at 27.3 V/sub RMS/ on the 1.5-mm diameter output tip, amounting to 25,600 degree/s vibration velocity along the outer circumference of the tip. At 1.02 MHz, a torsional vibration velocity of 1750 mm/s (134,000 degree/s) at 17.8 V/sub RMS/ was obtained through use of the thickness mode of the PZT elements. Using the design described in this study, high-power torsional transducers with diameters of 5 mm and below are now possible.

Using a 3×4×5 mm torsional microtransducer attached to a 30-cm long, 0.3-mm diameter flexible stainless steel wire, torsional vibration and coupled torsional-flexural vibration is transmitted to a remotely-placed rotor. The torsional microtransducer uses flat, thickness-poled lead zirconate titanate (PZT) elements attached to the surface of a square-sided prism with a tapered horn and tip; the elements twist the structure and generate torsional vibration amplified by the horn and tip at 150–260 kHz. Swaged to the wire–the `acoustic waveguide'–torsional vibration is transmitted into the wire, and flexural vibration is developed in the wire due to strong torsional-flexural coupling, demonstrated by measurement of the vibration velocity. Standing wave vibration was generated (standing wave ratio, SWR≈7.5) in the waveguide with nothing on the waveguide tip, but upon using a rotor, traveling wave vibration transmitted energy to the rotor (SWR≈4), which acted essentially as a loss; by placing a damping material on the tip instead of a rotor, very similar traveling wave motion was obtained (SWR≈1.5). The few torsional resonances of the transducer were found to be greatly increased in number by the waveguide, and rotors, with a contact radius of 300 µm, were found to rotate for most of these resonances in either direction at up to 11,500 rpm and 3.5 µN-m.

The ultrasonic air pump with a bending vibrator and a reflector was discussed. Simulation method to calculate the acoustic streaming in the air gap of the pump is important for the design. We suggest three methods to analyze the acoustic streaming on our ultrasonic air pump and compared these calculated and experimental results in the sound pressure distribution and the flow velocity distribution in the air gap. By ignoring one axis component and keeping the mesh fineness, FEA result improved in preciseness.