Preface

In the twenty-first century, bearings are expected to perform better in the form of various operating conditions, that is from low speed to extremely high speed and from low load to huge load applications. The expectations from the field of bearing technology are great. Dur‐ ing the recent years, we have been witnessing the development of a new generation of me‐ chanical systems that are highly miniaturized and very sophisticated, yet extremely robust. Technological progress creates increasingly arduous conditions for rolling mechanisms. Ad‐ vances in many fields including aeronautics, space and atomic power involve extreme operat‐ ing speeds, temperatures and environments. Moreover, rolling bearings are used in diverse precision machinery operations, for example, the high-load, high-temperature, dusty envi‐ ronment of steel making; the dirty environments of earthmoving and farming; the life-critical applications in aircraft power transmissions and the extreme low to high temperature and vacuum environments of deep space. They perform well in all of these applications.

Most information and data pertaining to the performance of rolling bearings are presented in manufacturer's catalogues. These data are almost entirely empirical in nature or informa‐ tion contained in International Organization for Standards (ISO) or similar publications. These data pertain only to applications involving slow speed, simple loading and nominal operating temperatures. If an engineer wishes to evaluate the performance of bearing appli‐ cations operating beyond these bounds, it is necessary to return to the basics of rolling and sliding motions. Particularly since 1960, much research has been conducted for rolling bear‐ ings and rolling contact phenomena. In this modern age of deep-space exploration and cy‐ berspace, many different kinds of bearings have come into use. Each of these bearing types excels in some specialized field of application.

Chapter 1 deals with the new concept for the design of a micro-GT support system. Instead of using a single type of bearing as usual, the new system includes different types, in order to take advantage of the best characteristics of each one and, simultaneously, to minimize the effects of the relevant flaws. The second chapter presents an electromagnetic levitation system for active magnetic bearing wheels. A meaningful electromagnetic force by using the singular value decomposition is also derived, and numerical simulation and experimental results on the control of the electromagnetic levitation system are discussed. Chapter 3 presents a general overview of various condition monitoring and fault diagnosis techniques for rolling-element bearings in the current practice and shows the pros and cons of each technique. The techniques introduced in this chapter include data acquisition techniques, major parameters used for bearing condition monitoring, signal analysis techniques and bearing fault diagnosis techniques using either statistical features or artificial intelligent tools. Chapter 4 examines different types of bearing supports. Technical parameters of dif‐ ferent types of bearing supports are presented. The effectiveness of some types of bearings is

determined. General approach for the calculation of bearing overall dimensions is consid‐ ered. In Chapter 5, motor current signature analysis based on squared envelope spectrum is applied in order to identify and to estimate the severity of outer race bearing faults in induc‐ tion machine. Bearing fault characteristic components are extracted combining summation of phase currents, pre-whitening, spectral kurtosis and squared envelope spectrum analysis.

I have endeavoured to maintain the material presented in an up-to-date and useful format. I hope that the readers especially young researchers and engineers in this field will find this book as useful and informative. I feel amazing pleasure to edit this book. I would like to express my sincere gratitude to all authors for their outstanding chapters. I also wish to ac‐ knowledge the InTech editorial staff, in particular, Mr. Edi Lipovic, Publishing Process Man‐ ager, for indispensable technical assistance in book preparation and publishing. And of course, I would like to thank my parents, wife Veera and loving son Fagun for the support they always gave to me—thanks for being close to me during all my life.

#### **Prof. (Dr.) Pranav H. Darji**

Professor and Head, Department of Mechanical Engineering C. U. Shah College of Engineering and Technology

> Director, P. G. Studies and Research Research, Development and Innovation Centre C. U. Shah University Wadhwan City, Gujarat (India)
