**3.3 Thermal performance of USM**

Performance of Ultrasonic motors in extreme temperature setting is the key challenge faced by various researchers. Thus, Nishizawa et al. developed spherical ultrasonic motor for space application & investigated for the durability to the radiant heat from the sun [256]. Drive performance was conducted for estimated duration more than 70 mins for higher than +120°C conditions. In order to maintain its drive performance, selection of piezoelectric elements & adhesive materials were significantly discussed. [256], further spherical USM was investigated in low temperature environment of −80°C, & approximately 60 minutes cumulative drive time was achieved by applying the same piezoelectric element and the adhesive materials utilized for high temperature conditions [257]. Shi et al., presented a general optimum frequency tracking scheme for an ultrasonic motor, which no longer required the amplitudes of the applied voltages to keep identical [258]. The mechanical quality factor of an ultrasonic motor was initially derived to describe


*The Roles of Piezoelectric Ultrasonic Motors in Industry 4.0 Era: Opportunities & Challenges DOI: http://dx.doi.org/10.5772/intechopen.100560*


#### **Table 4.**

*Listed of the research articles (2015–2020) on the applications of USM.*

the loss, which further was also in proportion to the temperature rise. The optimum frequency from the loss reduction viewpoint was then obtained, at which frequency the ultrasonic motor maintained the minimum loss and subsequently the minimum temperature rise. Sunif et al., presented heat energy modeling method for determining and characterizing of a piezoelectric stator profile that applied in a piezoceramic ultrasonic motor with the consideration of heat generated [259]. A thermal analysis was conducted in order to analyze the heat distribution on the stator & results showed different longitudinal deflection with the increment of the

temperature. Liu et al. studied the temperature variations of different components under different driving voltages for a high-power longitudinal-longitudinal hybrid type T shaped ultrasonic motor [260]. Cheng et al. described about hypothesis that a temperature gradient transverse to the wave propagating direction could significantly increase the working velocity of acoustic streaming-driven motors which was then investigated by numerically solving the hydrodynamic equations & it was found that the velocity of the rotor only weakly depends on the transverse temperature gradient, the velocity increased by only ~8.8% for temperature difference of 40°C between the rotor and the stator [261]. Nakazono et al., studied temperature dependence of USM in cryogenic conditions [262]. Ultrasonic transducer comprising of a body & nut made of SUS304 & bolt made of titanium was fabricated & evaluated in the temperature range of 45 to 293 K. It was proved that when titanium was used for clamping bolt of the transducer, the motor can be driven without the regulation of the preload.] Lv et al., developed a novel theoretical model to investigate the temperature field and output characteristics of a standing wave ultrasonic motor [263]. The results showed that the developed model can not only predict the temperature variation of motor in continuous operation but also evaluate the influence of surface roughness and various input parameters on output characteristics of motor.

We reviewed some literature review papers published on ultrasonic motors. We found author Peng et al. reviewed literature & provided summary on precision piezoelectric motors over long ranges based on the principle of repeating a series of small periodic step motions, named "frequency leveraged motors" [264]. Work was classified into three categories by different frequency driving methods, including ultrasonic motors, quasi-static motors, and motors combined resonant and quasistatic operations. A comprehensive summary of piezoelectric motors, with their classification from initial idea to recent progress, was presented by Spanner and Koc [265]. This review also includes some of the industrial and commercial applications of piezoelectric motors that are presently available in the market as actuators. Peled et al., reviewed & provided summary of the design of high precision motion solutions based on L1B2 (first longitudinal and second bending modes) ultrasonic motors—from the basic motor structure to the complete motion solution architecture, including motor drive and control, material considerations and performance envelope [266]. Gao et al., presented recent progress in nonresonance piezoelectric actuators with the working principles and properties of actuators and the piezoelectric materials and configurations, fabrication, and applications [267].

## **3.4 Ultrasonic motors applications**

The **Table 4** illustrates about various research articles published on the ultrasonic motor applications.
