**1. Introduction**

Increasing functionalities and weights/sizes reductions are critical issues for future aircrafts, space exploration vehicles, space instrumentations and industrial application etc. One challenge is the miniaturization of motors, wherein the efficiency of commonly used electromagnetic coil-based motors is dramatically reduced when their size less than centimeters scales. On the other hands, the rapid developments on piezoelectric ultrasonic motors (USMs) may fill the technical gap. Piezoelectric ultrasonic motors have been used in various technological fields from past decade in the gadgets, which we are using in our daily life i.e., a mobile phone to most advanced applications in aerospace. Recent advanced sciences & technologies developments on complex & tech-savvy products like satellites, mobile phones, camera lens, spaceships, automotive, robotics, biomedical instruments, manufacturing, etc., makes our life more convenient. These new products have raised new demands on modern motors like micro scale, light weight, high torque, no electromagnetic interference, low noise etc., which cannot be met by traditional

motors. To make bridge for this gap, many scientists developed specialized motors, such as electrostatic motors, USMs, bionic motors, photo-thermal motors, shape memory alloy motors, microwave motors, etc. Among them, USMs have more advantages [1].

Although the first concept of USMs was invented in 1948, when just after the World War II, USMs have been used for practical applications in 1980s. It works on the principle of converse piezo electric effect *i*.*e*., vibrations occur when an electrical field is applied to some piezoelectric structures. Similar to traditional electromagnetic motors this kind of motors comprises of stator & rotor, however, the difference is that a USM consists of piezoelectric structure, which is bonded to stator instead of coil and magnet pairs to make simpler and compact in size. In USMs, the piezoelectric structure is first vibrated in ultrasonic frequency band (>20 kHz), which in turn vibrates the stator when a driving voltage is applied in matched frequency. Thus, the frictional contact force between the stator & rotor or slider leads to the mechanical movement & torque. USMs can obtain high torque/weight ratio (torque density) in comparison with traditional electromagnetic motors because they are compact in structure & flexible in design. They are capable to drive the payloads directly without connecting to gear or gear train mechanism for some special applications. Most important that USMs quickly response commends in less than a few microseconds due to the advantages of piezoelectric materials and small inertia of rotors. Furthermore, they have capability of self-locking, high holding torque, precision motion control which can be utilized for application areas requiring high degree of precise motion for, e.g., medical operations & manufacturing or inspection of intricate products. In addition, USMs have zero electromagnetic interference which is one of the prominent applications in magnetic resonance imaging (MRI). USMs can also be operated in extreme temperature conditions which makes them first choice to use in aerospace application for e.g., space mission. Apart from above, they are silent during their operating cycle which makes them suitable for low noise applications [1].

Although USMs has many advantages, there are still several challenges remaining to achieve them in key areas like new design, motion control, piezoelectric material, friction & wear, thermal performance, modeling & optimization and advanced manufacturing technologies [2]. These challenges needed to be addressed in order to make USMs to be broadly utilized with its full potential in modern day industrial settings & diverse field of applications.

Fourth Industrial revolution or Industry 4.0 is the current phase of the industry wherein its emphasis on the digitization & interconnection of the products & services throughout the product life cycle i.e., from the birth of the product to the end of the life of product/services. Industry 4.0 relies mainly on various technological tools, which include but not limited to Big Data & AI analytics, Augmented reality (AR) Additive Manufacturing, Cyber Security, Industrial Internet of Things (IIoT), Autonomous Robots, Digital Twins, Horizontal & Vertical integrations & Cloud computing for carrying out the process of digitization & interconnection. Therefore, in this article, we not only take advantage of Industry 4.0 tools to improve the performance of the USMs but also promote the applications of USMs that can make them best fit into Industry 4.0 settings.

This chapter is divided into five sections. In the first section, we will introduce the history of development of USMs, types of USMs, structure & operating mechanism of USMs, and piezoelectric materials used. In the second section, the reviews of various articles, especially the publications in the last 5 years on ultrasonic motors from eclectic sources i.e., conference proceedings, journals, US patents & doctoral thesis. It analyses them & gives a brief bibliographic summary comprising of publication year, journal of publication, country of origin of research. The

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

classification of USM technologies in different categories, which include mainly new design, motion control, piezoelectric material, friction & wear, thermal performance, modeling & optimization & provide comprehensive summary of the articles describing achievements, challenges & opportunities, will be presented in the third section. The fourth Section of this chapter will briefly introduce industry 4.0 & key enabling technologies, i.e., Big Data & Artificial Intelligence analytics, Augmented Reality, Additive manufacturing, Industrial internet of things (IIoT), Digital Twins & simulation. In the Fifth section, it will be addressed that the approaches to improve the overall performance of piezoelectric motors by effective utilizing key enabling technologies offered in Industry 4.0 settings. It further elaborates on the various types & applications of piezoelectric motors that can be utilized effectively to foster Industry 4.0 expectations.
