Piezoelectric ultrasonic motor

The use of this motor in direct drive means that the complete function is obtained without any additional gear mechanism (for speed reduction, or for converting rotation in translation). Optics is probably the domain where the use of the piezoelectric motors is the most advanced. The most famous example, is the Canon camera, which includes an auto focus zoom based on a piezoelectric ultrasonic motor (USM) since 1992 (Fig. 6.21) [12]. 

Following a principle used in piezoelectric ultrasonic motors [60], T. Aku-ta [61] has built the first magnetostrictive friction motor. This stator is made of pairs of orthogonal actuators excited with sinusoidal 90° phase-shift currents, which produce an elliptical vibration. The modeling of such magnetostrictive stators [42] has shown that in quasi-static operation a good elliptical motion is produced. It has also been shown that there are many coupled modes, but none of them provides a satisfactory elliptical motion. Therefore, unlike piezoelectric motors, this motor cannot operate at resonance. As a consequence and in relation to the previous analysis of power (Fig. 6.34), the efficiency is comparatively weak. Its other characteristics are a speed of 40°/s and a torque of 1.8 Nm [62]. 

Uchino, K. (1997) Piezoelectric Actuators and Ultrasonic Motors, Kluwer Academic Publishers, London. 

Uchino K (1996) Piezoelectric actuators and ultrasonic motors. Kluver Academic, Boston... 

Piezoelectric and electrostrictive devices have become key components in smart actuator systems such as precision positioners, miniature ultrasonic motors and adaptive mechanical dampers. This section reviews the developments of piezoelectric and related ceramic actuators with particular focus on the improvement of actuator materials, device designs and applications of the actuators. 

The material requirements for these classes of devices are somewhat different, and certain compounds will be better suited to particular applications. The ultrasonic motor, for instance, requires a very hard piezoelectric with a high mechanical quality factor Qm, to suppress heat generation. Driving the motor at the antiresonance frequency, rather than at resonance, is also an intriguing technique to reduce the load on the piezoceramic and the power supply [42]. The servo displacement transducer suffers most from strain hysteresis and, therefore, a PMN electrostrictor is used for this purpose. The pulse drive motor requires a low permittivity material aimed at quick response with a certain power supply rather than a small hysteresis, so soft PZT piezoelectrics are preferred rather than the high-permittivity PMN for this application. 

Tokin developed a piezoelectric ceramic cylinder for a torsional vibrator [61]. Using an interdigital type electrode pattern printed with a 45° cant angle on the cylinder surface, torsion vibration was generated, which is applicable for a simple ultrasonic motor. 

Tabib-Azar M (1998) Microactuators, electrical, magnetic, thermal, optical, mechanical, chemical and smart structures. Kluwer, Norwell, MA Uchino K (1997) Piezoelectric actuators and ultrasonic motors. Kluwer, Norwell, MA Uchino K (2000) Ferroelectric devices, Marcel Dekker, New York... 

Piezomotors can produce elliptical motions either at the mechanical resonance (leading to ultrasonic motors) or in quasistatic (leading to stepping piezoelectric motors, so-called Inchworm ) [14]. 

The first linear micromotor, based on magnetostrictive thin films deposited on a 7 pm polyamide film, was built in Japan in 1994 [66]. The 13 mm long protot3rpe used a 200 Hz vibration induced by magnetostriction to obtain one-way motion at 5 imn/s. This is a mode conversion ultrasonic motor (MCUM) according to the Japanese classification of piezoelectric motors. 

Uchino, K. (1995) Piezoelectric Actuators and Ultrasonic Motors. Electronic Materials Science Technology (ed. H.L. Tuller), Kluwer Academic Publ., Deventer. ISBN 978-07923-98-11-0, 354 pp. 

Kanda, T., Makino, A., Suzumori, L., Morita, T. and Kurosawa, M.K. (2004) A cylindrical micro ultrasonic motor using a micro-machined bulk piezoelectric transducer , in IEEE Ultrasonics Symposium, Montreal, Canada 1298-1301. 

K. Uchino, Piezoelectric Actuators and Ultrasonic Motors, Kluwer Academic Publishers (1997) B. Jaffe, W. R. Cook and H. Jaffe, Piezoelectric Ceramics, Academic Press (1971). 

A compact ultrasonic rotory motor, as tiny as 3 mm in diameter, has been developed at the Pennsylvania State University. As shown in Figure 4.1.37, the stator consists of a piezoelectric ring and two concave/convex metal endcaps with windmill shaped slots bonded together, so as to generate a coupling of the up-down and torsional vibrations [60]. Since the number of components is reduced and the fabrication process is much simplified, the fabrication price is decreased remarkably, and a disposable design becomes feasible. When driven at 160 kHz, a maximum revolution of 600 rpm and a maximum torque of 1 mN m were obtained for a 11 mm diameter motor. 

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