diagnostic maintenance and monitoring of machines1

Diagnostic Maintenance and Monitoring of Machines

Indian Institute of Technology Roorkee

UG Course Diagnostics Maintenance & Monitoring of MachinesCourse Objectives To introduce undergraduate student to the concept ofdiagnostics for detection of faults that are most oftenencountered in practice in industry Awareness about the existing vibration and noise basedfault detection and other conventional monitoring techniques Their applications and economic benefits

Credits: 4

Weekly Engagement: 3-1-2/2

Course Teacher: SPH

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UG Course Diagnostics Maintenance & Monitoring of MachinesCourse Objectives To introduce undergraduate student to the concept ofdiagnostics for detection of faults that are most oftenencountered in practice in industry Awareness about the existing vibration and noise basedfault detection and other conventional monitoring techniques Their applications and economic benefits

Credits: 4

Weekly Engagement: 3-1-2/2

Course Teacher: SPH

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The desire and need for accurate diagnostic and realpredictive prognostic capabilities have been around for as

long as human beings have operated complex and expensive

machinery.

The area of intelligent maintenance and diagnostic andprognosticenabled condition-based maintenance (CBM) of

machinery, is a vital one for todays complex systems in

industry, aerospace vehicles, military and merchant ships, the

automotive industry, and elsewhere.

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Cont..

For fault detection, the ability is specified to detectmechanical system degradation below required performancelevels (incipient or impending failure) owing to physicalproperty changes through detectable phenomena.

The industrial and military communities are concernedabout critical system and component reliability andavailability. The goals are both to maximize equipment uptime and to minimize maintenance and operating costs.

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Six-stage diagnostics process

1. Verify the fault

2. Collect further information

3. Evaluate the evidence

4. Carry out further tests in a logical sequence

5. Rectify the problem

6. Check all systems.

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The art of diagnostics:

The knowledge needed for accurate diagnostics is in twoparts:1. understanding of the system in which the problem exists;2. having the ability to apply a logical diagnostic routine.

Diagnostics Routine

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Mechanical diagnostic techniques

1. Check first the obvious faults

Start all hands on diagnostic routines with hand and eyechecks. In other words look over the vehicle for obviousfaults.

If the engine is blowing blue smoke out of the exhaust consider the worth of tracing the cause of a tapping noise inthe engine!

When an engine will not start check that there is fuel inthe tank!

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Cont

2. Noise, vibration and harshness

Noise, vibration and harshness (NVH) concerns havebecome more important as drivers have become moresensitive to these issues. Drivers have higher expectations ofcomfort levels. The main areas of the vehicle that produceNVH are:

tyres;

engine accessories;

suspension;

driveline.

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Cont

3. Noise conditions

Noise is very difficult to describe. Gear noise is typically a howling or whining due to geardamage or incorrect bearing preload.It can occur at various speeds and driving conditions, or itcan be continuous. Chuckle is a rattling noise that sounds like a stick heldagainst the spokes of a spinning bicycle wheel. It usuallyoccurs while decelerating. Knock is very similar to chuckle though it may be louderand occurs on acceleration or deceleration.

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Cont

4. Vibration conditions

Clicking, popping or grinding noises may be noticeable at low speeds and be caused by the following: inner or outer joints worn (often due to lack of lubrication so check for split gaiters); loose drive shaft; another component contacting a drive shaft; damaged or incorrectly installed wheel bearing, brake or suspension component.The following may cause vibration at normal road speeds: out-of-balance wheels; out-of-round tyres.

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Auxiliary diagnostics system analysis

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Engine Control with Self Diagnostics

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References

1. Sound and Vibration book, KTH, Stockholm, 2006.

2. Collacott, R.A., Mechanical fault diagnosis and conditionmonitoring, Chapman & Hall, 1977.

3. Davies, M., Handbook of condition monitoring-Techniques and Methodology, Springer, 2006.

4. John H. Williams, Alan Davies, Paul R. Drake, Condition-Based Maintenance and Machine Diagnostics, Springer,2006.

5. B. K. N. Rao, Handbook on Condition Monitoring, ElsevierScience, 1998.

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Contents Introduction Typical defects in gears and rolling element bearings Vibrations of gears and bearings Monitoring methods Vibration analysis Sound monitoring Discrete frequencies Machine condition indicators Measurement techniques Signal processing tools Case studies

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Chapter 1: Introduction

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Maintenance Philosophies

Corrective maintenance

Preventive maintenance

Condition based maintenance

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Cont

Corrective Maintenance:

Run to failure

The maintenance is done after some part breaks.

Maintenance costs are low.

Operating costs are high because of the downtime

and damages.

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Cont

Preventive Maintenance:

Scheduled maintenance action.

Schedule is created from lifetime statistics of

similar machines.

High maintenance costs due unnecessary

maintenance actions.

Possibility to equipment failures.

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Cont

Condition Based Maintenance:

Maintenance when required

Unnecessary maintenance is avoided.

Availability of the equipment is guaranteed

Overall cost of maintenance is reduced

Monitoring creates costs.

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Total Cost of Maintenance

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Cont

Architecture for condition based maintenance

Open System Architecture for Condition BasedMaintenance (OSA-CBM)

ISO 13374-1&2 Condition monitoring and diagnostics of

machines Data processing, communication and

presentation

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Fault Detection and Isolation (FDI)

FDI methods Data-driven Based on data measured from the model Statistical Process Control (SPC), Principal Component Analysis (PCA), Artificial Neural Networks (ANN) Analytical Based on detailed mathematical models Parameter estimation, Observers, Parity relations Knowledge-based Based on qualitative models Causal analysis, Signed directed graph, Expert systems, Case based reasoning, ANN

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Introduction to Condition Based Maintenance

Condition-based maintenance (CBM) is the use ofmachinery run-time data to determine the machinerycondition and hence its current fault / failure condition, whichcan be used to schedule, required repair and maintenanceprior to breakdown.

CBM is based on detecting causes or symptoms of afuture failure so that it can be handled most cost effectivelybefore its occurrence.

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Condition-based maintenance (CBM) is a methodologythat strives to identify incipient faults before they becomecritical in order to enable more accurate planning ofpreventive actions.

By using efficient maintenance policies, a number ofsystem improvements can be realized, includingimprovements to system performance, productivity, reliabilitymetrics, cost, and cost-related metrics.

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Advantages of CBM

A well-orchestrated program will all but eliminatecatastrophic equipment failures.

Maintenance activities can be scheduled to minimize oreliminate overtime costs.

Additionally, inventory can be minimized because parts orequipment will not have to be ordered ahead of time to

support anticipated maintenance needs.

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Cont

With equipment operating at an optimal level, energy costsare reduced and plant reliability is increased.

Importantly, CBM not only reduces the amount ofmaintenance performed but also avoids maintenance-

induced failures.

However, existing CBM models have many limitations thatprevent them from effectively modeling all kinds of complex

situations that arise in CBM decision-making.

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Value potential of CBM

As systems get more costly, instrumentation andinformation systems tend to become more cheap andreliable, CBM becomes an important tool for running a plantor factory in an optimal manner. More optimal operations will lead to lower production costand lower use of resources. And lower use of resources maybe one of the most important differentiators in a future whereenvironmental issues become more important by the day. A more down to earth scenario where value can becreated is by monitoring the health of your car motor. Ratherthan changing parts at predefined intervals, the car itself cantell you when something needs to be changed based oncheap and simple instrumentation.

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Categorization of application of CBM technologies

Region I - High Cost / Low Effectiveness: Do notimplement technology. For mission critical applications (e.g.

as identified in RCM / FMECA analysis) use otherapproaches (e.g. time based maintenance) to ensure

functionality / reliability of equipment.

Region II - High Cost / High Effectiveness: Only implementtechnology on mission critical equipment and only if other

more effective / lower cost CBM technologies are not

available.

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Cont

Region III - Low Cost / Low Effectiveness: Only implementtechnology in mission critical applications as a confirmatory

technology in conjunction with more effective technologies or

where no other CBM technology is feasible. For non-critical

applications, implement only if quantitative calculations

indicate an acceptable return on investment can be achieved.

Region IV - Low Cost / High Effectiveness: Implementtechnology wherever practicable. Implement in all

applications except those specifically identified as run-to

failure.

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Cont

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Indian Institute of Technology Roorkee 31

UG Course Diagnostics Maintenance & Monitoring of Machines UG Course Diagnostics Maintenance & Monitoring of MachinesSlide Number 3Cont..Six-stage diagnostics processThe art of diagnostics:Mechanical diagnostic techniques ContContContAuxiliary diagnostics system analysisEngine Control with Self DiagnosticsReferences ContentsChapter 1: IntroductionMaintenance PhilosophiesContContContTotal Cost of MaintenanceContFault Detection and Isolation (FDI)Introduction to Condition Based MaintenanceSlide Number 24Advantages of CBMContValue potential of CBMCategorization of application of CBM technologiesContContSlide Number 31

diagnostic maintenance and monitoring of machines1

Documents

sph1diagnostic maintenance

sph2diagnostic maintenance

diagnostic routines

logical diagnostic routine

accurate diagnostics

detection of faults

noise basedfault detection

course teacher