Vibration-based Condition Monitoring

Transcription

1 RED BOX RULES ARE FOR PROOF STAGE ONLY. DELETE BEFORE FINAL PRINTING. Industrial, Aerospace and Automotive Applications Robert Bond Randall School of Mechanical and Manufacturing Engineering, University of New South Wales, Australia Without doubt the best modern and up-to-date text on the topic, written by one of the world leading experts in the field. Should be on the desk of any practitioner or researcher involved in the field of Machine Condition Monitoring. Simon Braun, Israel Institute of Technology Explaining complex ideas in an easy to understand way, Vibration-based Condition Monitoring provides a comprehensive survey of the application of vibration analysis to the condition monitoring of machines. Reflecting the natural progression of these systems by presenting the fundamental material and then moving onto detection, diagnosis and prognosis, Randall presents classic and state-of-the-art research results that cover vibration signals from rotating and reciprocating machines, basic signal processing techniques, fault detection, diagnostic techniques, and prognostics. Developed out of notes for a course in machine condition monitoring given by Robert Bond Randall over ten years at the University of New South Wales, Vibration-based Condition Monitoring is essential reading for graduate and postgraduate students/ researchers in machine condition monitoring and diagnostics as well as condition monitoring practitioners and machine manufacturers who want to include a machine monitoring service with their product. Includes a number of exercises for each chapter, many based on MATLAB, to illustrate basic points as well as to facilitate the use of the book as a textbook for courses in the topic. Accompanied by a website housing exercises along with data sets and implementation code in MATLAB for some of the methods as well as other pedagogical aids. Authored by an internationally recognised authority in the area of condition monitoring. Enjoyed this book? Cover design by Dan Jubb Why not tell others about it and write a review on your favourite online bookseller. Randall Vibration-based Condition Monitoring Vibration-based Condition Monitoring Robert Bond Randall Vibration-based Condition Monitoring Industrial, Aerospace and Automotive Applications

2

3 VIBRATION-BASED CONDITION MONITORING

4

5 VIBRATION-BASED CONDITION MONITORING INDUSTRIAL, AEROSPACE AND AUTOMOTIVE APPLICATIONS Robert Bond Randall School of Mechanical and Manufacturing Engineering, University of New South Wales, Australia A John Wiley and Sons, Ltd., Publication

6 This edition first published 2011 C 2011 John Wiley & Sons, Ltd Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. MATLAB R is a trademark of The MathWorks, Inc., and is used with permission. The MathWorks does not warrant the accuracy of the text or exercises in this book. This book s use or discussion of MATLAB R software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of MATLAB R software. Library of Congress Cataloging-in-Publication Data Randall, Robert Bond. Vibration-based condition monitoring : industrial, aerospace and automotive applications / Robert Bond Randall. p. cm. Includes index. ISBN (hardback) 1. Vibration Testing. 2. Nondestructive testing. 3. Vibration Measurement. I. Title. TA355.R dc A catalogue record for this book is available from the British Library. Print ISBN: epdf ISBN: obook ISBN: epub ISBN: Typeset in 10/12pt Times by Aptara Inc., New Delhi, India

7 To my daughters Katrina and Deborah.

8

9 Contents Foreword About the Author Preface xi xiii xv 1 Introduction and Background Introduction Maintenance Strategies Condition Monitoring Methods Vibration Analysis Oil Analysis Performance Analysis Thermography Types and Benefits of Vibration Analysis Benefits Compared with Other Methods Permanent vs Intermittent Monitoring Vibration Transducers Absolute vs Relative Vibration Measurement Proximity Probes Velocity Transducers Accelerometers Dual Vibration Probes Laser Vibrometers Torsional Vibration Transducers Shaft encoders Torsional Laser Vibrometers Condition Monitoring the Basic Problem 20 References 23 2 Vibration Signals from Rotating and Reciprocating Machines Signal Classification Stationary Deterministic Signals Stationary Random Signals Cyclostationary signals 30

10 viii Contents 2.2 Signals Generated by Rotating Machines Low Shaft Orders and Subharmonics Vibrations from Gears Rolling Element Bearings Bladed Machines Electrical Machines Signals Generated by Reciprocating Machines Time Frequency Diagrams Torsional Vibrations 60 References 61 3 Basic Signal Processing Techniques Probability Distribution and Density Fourier Analysis Fourier Series Fourier Integral Transform Sampled Time Signals The Discrete Fourier Transform The Fast Fourier Transform Convolution and the Convolution Theorem Zoom FFT Practical FFT Analysis Hilbert Transform and Demodulation Hilbert Transform Demodulation Cepstrum Analysis Terminology and Definitions Typical Applications of the Cepstrum Practical Considerations with the Cepstrum Digital Filtering Realization of Digital Filters Deterministic/Random Signal Separation Order Tracking Time Synchronous Averaging Linear Prediction Adaptive Noise Cancellation Self-adaptive Noise Cancellation Discrete/Random Separation DRS Time Frequency Analysis The Short Time Fourier Transform The Wigner Ville Distribution Wavelet Analysis Cyclostationary Analysis and Spectral Correlation Spectral Correlation 135

11 Contents ix Spectral Correlation and Envelope Spectrum Wigner Ville Spectrum 139 References Fault Detection Introduction Rotating Machines Vibration Criteria Use of Frequency Spectra CPB Spectrum Comparison Reciprocating Machines Vibration Criteria for Reciprocating Machines Time Frequency Diagrams Torsional Vibration 160 References Diagnostic Techniques Harmonic and Sideband Cursors Examples of Cursor Application Minimum Entropy Deconvolution Spectral Kurtosis and the Kurtogram SK Definition and Calculation Use of SK as a Filter The Kurtogram Gear Diagnostics Techniques Based on the TSA Transmission Error as a Diagnostic Tool Cepstrum Analysis Separation of Spalls and Cracks Diagnostics of Gears with Varying Speed and Load Rolling Element Bearing Diagnostics Signal Models for Bearing Faults A Semi-automated Bearing Diagnostic Procedure Reciprocating Machine and IC Engine Diagnostics Time Frequency Methods Cylinder Pressure Identification 217 References Fault Trending and Prognostics Introduction Trend Analysis Trending of Simple Parameters Trending of Impulsiveness Determination of Spall Size in Bearings Advanced Prognostics Physics-Based Models 244

12 x Contents Data-Driven Models Hybrid Models 247 References 250 Appendix: Exercises and Tutorial Questions 253 A.1 Introduction and Background 253 A.1.1 Exam Questions 253 A.2 Vibration Signals from Machines 254 A.2.1 Exam Questions 254 A.3 Basic Signal Processing 256 A.3.1 Tutorial and Exam Questions 256 A.4 Fault Detection 270 A.4.1 Tutorial and Exam Questions 270 A.4.2 Assignment 273 A.5 Diagnostic Techniques 275 A.5.1 Tutorial and Exam Questions 275 A.5.2 Assignments 280 A.6 Prognostics 284 A.6.1 Tutorial and Exam Questions 284 Index 285

13 Foreword Robert Randall uses state-of-the-art vibration measurement and analysis in this book about condition-based monitoring of machinery; other forms of condition monitoring, including oil analysis and infrared thermography are briefly described. The text is the result of the author s years of involvement in the development, practice, and teaching of techniques used in the field, including contributions to digital signal analysis. A highly sophisticated methodology for assessing machine condition has evolved in the last 70 years with respect to techniques, digital instruments, and computer chips. Despite many years of effort, the technique that every maintenance manager yearns for prognostics (run time to failure) does not yet exist in a usable form. However, condition monitoring of machinery using vibration measurements and analysis is a major component of all manufacturing processes (chemical, petroleum, automobile, paper, and power) as well as military and airline operations. The relationship between vibration signals and machine condition was first recognized by Rathbone in his 1939 paper on Vibration Tolerance. The Rathbone chart that appeared in the paper was a plot of amplitude versus frequency based on the concept that machine condition is related to vibration amplitude. His zones of severity (six db apart) were based on constant velocity and applied over the common frequency range of most machines. The chart was later refined by IRD Mechanalysis, the U.S. Navy, Blake, and others. Blake developed a chart containing plots of displacement, velocity, and acceleration versus frequency with severity levels spaced at 10 db and service factors for various machines. During this period simple meters and oscilloscopes were used to extract vibration levels from transducers. Overall vibration levels were used non-systematically until 1960 to identify machine condition. By this time it had been recognized that periodic monitoring could be useful in avoiding costly machine failures and improving return on investment. A meter and clipboard were used to measure and record vibration levels, another development the proximity probe by Bently for non-contacting shaft vibration measurement allowed permanent machine monitoring. Although screening involved overall vibration levels until the 1970s, vibration analysis expanded to address difficult and complex cases as a result of FFT analyzers that had greater resolution than analog filtered instruments. Portable tape recorders were used to acquire vibration data on defined routes; sometimes heavy analyzers were hauled into the field on carts and trucks. Blake and Jackson published the first texts related to condition monitoring in 1972 and 1979 respectively. Data collectors that use high-frequency accelerometers interfaced with digital computers were developed in the 1980s. They had a higher level of efficiency and effectiveness

14 xii Foreword and spurred development of new monitoring and analysis techniques using innovative signal processing. Recent improvements in condition monitoring include more sophisticated miniaturized data acquisition systems, physics and experience-based expert systems, Internet data sharing, and wireless data transmission. Unfortunately, progress with prognostic techniques has not produced practical techniques. Randall has written an authoritative monograph on state-of-the-art methods for evaluating the condition of machinery using vibration analysis. For the first time practitioners can refer to one source for the techniques commonly used. Because machines are complex and the range of application of signal processing techniques is wide, the user must be aware of their power and limitations. The text is interesting, well written, and well illustrated. This work on vibration signals, signal processing techniques, fault detection, diagnostic techniques, and fault trending and prognostics will provide guidance for individuals struggling to keep down maintenance costs on complex machines using the art and science of condition monitoring. Ronald L. Eshleman Vibration Institute Willowbrook, Illinois, USA October 2010

15 About the Author Bob Randall is a visiting Emeritus Professor in the School of Mechanical and Manufacturing Engineering at the University of New South Wales (UNSW), Sydney, Australia, which he joined as a Senior Lecturer in Prior to that, he worked for the Danish company Brüel & Kjær for 17 years, after 10 years experience in the chemical and rubber industries in Australia, Canada and Sweden. He was promoted to Associate Professor in 1996 and to Professor in 2001, retiring in He has degrees in Mechanical Engineering and Arts (Mathematics, Swedish) from the Universities of Adelaide and Melbourne, respectively. He is the invited author of chapters on vibration measurement and analysis in a number of handbooks and encyclopaedias and a member of the editorial boards of four journals, including Mechanical Systems and Signal Processing and Transactions of the IMechE Part C. He is the author of more than 190 papers in the fields of vibration analysis and machine diagnostics, and has supervised 14 PhD and 3 Masters projects to completion in those and related areas. Since 1996, he has been Director of the DSTO (Defence Science and Technology Organisation) Centre of Expertise in Helicopter Structures and Diagnostics at UNSW.