MAINTENANCE ENGINEERING

UNIT I PRINCIPLES AND PRACTICES OF MAINTENANCE PLANNING

Basic Principles of maintenance planning – Objectives and principles of planned maintenance

activity – Importance and benefits of sound Maintenance systems – Reliability and machine

availability – MTBF, MTTR and MWT – Factors of availability – Maintenance organization –

Maintenance economics.

INTRODUCTION

Maintenance Engineering is the discipline and profession of applying engineering

concepts to the optimization of equipment, procedures, and departmental budgets to achieve

better maintainability, reliability, and availability of equipment.

Maintenance, and hence maintenance engineering, is increasing in importance due to rising

amounts of equipment, systems, machineries and infrastructure.

Since the Industrial Revolution, devices, equipment, machinery and structures have grown

increasingly complex, requiring a host of personnel, vocations and related systems needed to

maintain them.

A person practicing Maintenance Engineering is known as a Maintenance Engineer.

OBJECTIVES AND PRINCIPLES:

Analysis of repetitive equipment failures.

Estimation of maintenance costs and evaluation of alternatives.

Forecasting of spare parts.

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Assessing the needs for equipment replacements and establish replacement programs

when due application of scheduling and project management principles to replacement

programs.

Assessing required maintenance tools and skills required for efficient maintenance of

equipment.

Assessing required skills required for maintenance personnel.

Reviewing personnel transfers to and from maintenance organizations assessing and

reporting safety hazards associated with maintenance of equipment.

Reliability may be defined in several ways:

The idea that an item is fit for a purpose with respect to time.

In the most discrete and practical sense: "Items that do not fail in use are reliable" and

"Items that do fail in use are not reliable".

The capacity of a designed, produced or maintained item to perform as required over

time.

The capacity of a population of designed, produced or maintained items to perform as

required over time.

The resistance to failure of an item over time.

The probability of an item to perform a required function under stated conditions for a

specified period of time.

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In line with the creation of safety cases for safety, the goal is to provide a robust set of

qualitative and quantitative evidence that an item or system will not contain unacceptable

risk.

The basic sorts of steps to take are to:

First thoroughly identify as many as possible reliability hazards (e.g. relevant System

Failure Scenarios item Failure modes, the basic Failure mechanisms and root causes) by

specific analysis or tests.

Assess the Risk associated with them by analysis and testing.

Propose mitigations by which the risks may be lowered and controlled to an acceptable

level.

Select the best mitigations and get agreement on final (accepted) Risk Levels, possible

based on cost-benefit analysis.

AVAILABILITY

A Reliability Program Plan may also be used to evaluate and improve Availability of a

system by the strategy on focusing on increasing testability & maintainability and not on

reliability.

Improving maintainability is generally easier than reliability. Maintainability estimates

(Repair rates) are also generally more accurate.

However, because the uncertainties in the reliability estimates are in most cases very

large, it is likely to dominate the availability (prediction uncertainty) problem; even in the

case maintainability levels are very high.

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When reliability is not under control more complicated issues may arise, like manpower

(maintainers / customer service capability) shortage, spare part availability, logistic

delays, lack of repair facilities, extensive retro-fit and complex configuration

management costs and others.

The problem of unreliability may be increased also due to the "Domino effect" of

maintenance induced failures after repairs.

Only focusing on maintainability is therefore not enough. If failures are prevented, none

of the others are of any importance and therefore reliability is generally regarded as the

most important part of availability.

One of the most important design techniques is redundancy.

RELIABILITY THEORY

Reliability is defined as the probability that a device will perform its intended function

during a specified period of time under stated conditions.

ACCELERATED TESTING:

The purpose of accelerated life testing is to induce field failure in the laboratory at a

much faster rate by providing a harsher, but nonetheless representative, environment.

In such a test, the product is expected to fail in the lab just as it would have failed in the field—

but in much less time.

The main objective of an accelerated test is either of the following:

To discover failure modes.

To predict the normal field life from the high stress lab life.

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Software reliability is a special aspect of reliability engineering. System reliability, by

definition, includes all parts of the system, including hardware, software, supporting

infrastructure (including critical external interfaces), operators and procedures. Traditionally,

reliability engineering focuses on critical hardware parts of the system. Since the widespread use

of digital integrated circuit technology, software has become an increasingly critical part of most

electronics and, hence, nearly all present day systems. Despite this difference in the source of

failure between software and hardware, several software reliability models based on statistics

have been proposed to quantify what we experience with software: the longer software is run, the

higher the probability that it will eventually be used in an untested manner and exhibit a latent

defect that results in a failure (Shooman 1987), (Musa 2005), (Denney 2005). As with hardware,

software reliability depends on good requirements, design and implementation. Software

reliability engineering relies heavily on a disciplined software engineering process to anticipate

and design against unintended consequences. There is more overlap between software quality

engineering and software reliability engineering than between hardware quality and reliability. A

good software development plan is a key aspect of the software reliability program. The software

development plan describes the design and coding standards, peer reviews, unit tests,

configuration management, software metrics and software models to be used during software

development.

Define objective and scope of the test

Collect required information about the product

Identify the stresses

Determine level of stresses

Conduct the accelerated test and analyze the collected data.

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MEAN TIME BETWEEN FAILURES

Mean time between failures (MTBF) is the predicted elapsed time between inherent

failures of a system during operation. MTBF can be calculated as the arithmetic mean (average)

time between failures of a system.

FORMAL DEFINITION OF MTBF

By referring to the figure above, the MTBF is the sum of the operational periods divided

by the number of observed failures.

If the "Down time" (with space) refers to the start of "downtime" (without space) and "up time"

(with space) refers to the start of "uptime" (without spMean time betMean time between

failuresween failuresace), the formula will be:

The MTBF is often denoted by the Greek letter θ, or

The MTBF can be defined in terms of the expected value of the density function ƒ(t)

where ƒ is the density function of time until failure – satisfying the standard requirement of

density functions –

The Overview

For each observation, downtime is the instantaneous time it went down, which is after

(i.e. greater than) the moment it went up, uptime. The difference (downtime minus uptime) is the

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amount of time it was operating between these two events. MTBF value prediction is an

important element in the development of products. Reliability engineers / design engineers, often

utilize Reliability Software to calculate products' MTBF according to various methods/standards.

However, these "prediction" methods are not intended to reflect fielded MTBF as is commonly

believed. The intent of these tools is to focus design efforts on the weak links in the design

MTTR

MTTR is an abbreviation that has several different expansions, with greatly differing

meanings. It is wise to spell out exactly what is meant by the use of this abbreviation, rather than

assuming the reader will know which is being assumed. The M can stand for any of minimum,

mean or maximum, and the R can stand for any of recovery, repair, respond, or restore. The most

common, mean, is also subject to interpretation, as there are many different ways in which a

mean can be calculated.

Mean time to repair

Mean time to recovery/Mean time to restore

Mean time to respond

Mean time to replace

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In an engineering context with no explicit definition, the engineering figure of merit,

mean time to repair would be the most probable intent by virtue of seniority of usage.

It is also similar in meaning to the others above (more in the case of recovery, less in the case of

respond, the latter being more properly styled mean "response time").

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UNIT II

MAINTENANCE POLICIES – PREVENTIVE MAINTENANCE

Maintenance categories – Comparative merits of each category – Preventive maintenance,

maintenance schedules, repairs cycle - Principles and methods of lubrication – TPM.

The maintenance is defined as follows: “the work of keeping something in proper

condition; upkeep.” This would imply that maintenance should be actions taken to prevent a

device or component from failing or to repair normal equipment degradation experienced with

the operation of the device to keep it in proper working order. For example, equipment may be

designed to operate at full design load for 5,000 hours and may be designed to go through 15,000

start and stop cycles. The wear-out period is characterized by a rapid increasing failure rate with

time. In most cases this period encompasses the normal distribution of design life failures.

The design life of most equipment requires periodic maintenance. Belts need adjustment,

alignment needs to be maintained, proper lubrication on rotating equipment is required, and so

on. In some cases, certain components need replacement, (e.g., a wheel bearing on a motor

vehicle) to ensure the main piece of equipment (in this case a car) last for its design life. Anytime

we fail to perform maintenance activities intended by the equipment’s designer, we shorten the

operating life of the equipment. But what options do we have? Over the last 30 years, different

approaches to how maintenance can be performed to ensure equipment reaches or exceeds its

design life have been developed in the United States. In addition to waiting for a piece of

equipment to fail (reactive maintenance), we can utilize preventive maintenance, predictive

maintenance, or reliability centered maintenance.

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Reactive Maintenance

Reactive maintenance is basically the “run it till it breaks” maintenance mode. No actions or

efforts are taken to maintain the equipment as the designer originally intended to ensure design

life is reached. Studies as recent as the winter of 2000 indicate this is still the predominant mode

of maintenance in the United States. The referenced study breaks down the average maintenance

program as follows:

>55% Reactive

31% Preventive

12% Predictive

2% Other.

Note that more than 55% of maintenance resources and activities of an average facility are

still reactive.

Advantages to reactive maintenance can be viewed as a double-edged sword. If we are

dealing with new equipment, we can expect minimal incidents of failure. If our maintenance

program is purely reactive, we will not expend manpower dollars or incur capital cost until

something breaks. Since we do not see any associated maintenance cost, we could view this

period as saving money. Our labour cost associated with repair will probably be higher than

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normal because the failure will most likely require more extensive repairs than would have been

required if the piece of equipment had not been run to failure. Chances are the piece of

equipment will fail during off hours or close to the end of the normal workday. If it is a critical

piece of equipment that needs to be back on-line quickly, we will have to pay maintenance

overtime cost. Since we expect to run equipment to failure, we will require a large material

inventory of repair parts. This is a cost we could minimize under a different maintenance

strategy.

Advantages

• Low cost.

• Less staff

Disadvantages

• Increased cost due to unplanned downtime of equipment.

• Increased labour cost, especially if overtime is needed.

• Cost involved with repair or replacement of equipment.

• Possible secondary equipment or process damage from equipment failure.

• Inefficient use of staff resources.

Preventive Maintenance

Preventive maintenance can be defined as follows: Actions performed on a time- or

machine-run-based schedule that detect, preclude, or mitigate degradation of a component or

system with the aim of sustaining or extending its useful life through controlling degradation to

an acceptable level.

While preventive maintenance is not the optimum maintenance program, it does have

several advantages over that of a purely reactive program. By performing the preventive

maintenance as the equipment designer envisioned, we will extend the life of the equipment

closer to design. This translates into dollar savings. Preventive maintenance (lubrication, filter

change, etc.) will generally run the equipment more efficiently resulting in dollar savings. While

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we will not prevent equipment catastrophic failures, we will decrease the number of failures.

Minimizing failures translate into maintenance and capital cost savings.

Advantages

• Cost effective in many capital-intensive processes

• Flexibility allows for the adjustment of maintenance periodicity.

• Increased component life cycle.

• Energy savings

• Reduced equipment or process failure

• Estimated 12% to 18% cost savings over reactive maintenance program.

Disadvantages

• Catastrophic failures still likely to occur.

• Labour intensive.

• Includes performance of unneeded maintenance.

• Potential for incidental damage to components

Predictive Maintenance

Predictive maintenance can be defined as follows: Measurements that detect the onset of

system degradation (lower functional state), thereby allowing causal stressors to be eliminated or

controlled prior to any significant deterioration in the component physical state. Results indicate

current and future functional capability.

Basically, predictive maintenance differs from preventive maintenance by basing

maintenance need on the actual condition of the machine rather than on some preset schedule.

You will recall that preventive maintenance is time-based. Activities such as changing lubricant

are based on time, like calendar time or equipment run time. For example, most people change

the oil in their vehicles every 3,000 to 5,000 miles travelled.

The advantages of predictive maintenance are many. A well-orchestrated predictive

maintenance program will all but eliminate catastrophic equipment failures. We will be able to

schedule maintenance activities to minimize or delete overtime cost. We will be able to minimize

inventory and order parts, as required, well ahead of time to support the downstream

maintenance needs. We can optimize the operation of the equipment, saving energy cost and

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increasing plant reliability. Past studies have estimated that a properly functioning predictive

maintenance program can provide a savings of 8% to 12% over a program utilizing preventive

maintenance alone. Depending on a facility’s reliance on reactive maintenance and material

condition, it could easily recognize savings opportunities exceeding 30% to 40%. In fact,

independent surveys indicate the following industrial average savings resultant from initiation of

a functional predictive maintenance program:

• Return on investment: 10 times

• Reduction in maintenance costs: 25% to 30%

• Elimination of breakdowns: 70% to 75%

• Reduction in downtime: 35% to 45%

• Increase in production: 20% to 25%.

Advantages

• Increased component operational life/availability.

• Allows for pre-emptive corrective actions.

• Decrease in equipment or process downtime.

• Decrease in costs for parts and labour.

• Better product quality.

• Improved worker and environmental safety.

• Improved worker morale.

• Energy savings.

• Estimated 8% to 12% cost savings over preventive maintenance program.

Disadvantages

• Increased investment in diagnostic equipment.

• Increased investment in staff training.

• Savings potential not readily seen by management.

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Reliability Centred Maintenance

Reliability centred maintenance (RCM) magazine provides the following definition of

RCM: “a process used to determine the maintenance requirements of any physical asset in its

operating context.”

The following maintenance program breakdowns of continually top-performing facilities

would echo the RCM approach to utilize all available maintenance approaches with the

predominant methodology being predictive.

• <10% Reactive

• 25% to 35% Preventive

• 45% to 55% Predictive.

Because RCM is so heavily weighted in utilization of predictive maintenance technologies,

its program advantages and disadvantages mirror those of predictive maintenance. In addition to

these advantages, RCM will allow a facility to more closely match resources to needs while

improving reliability and decreasing cost.

Advantages

• Can be the most efficient maintenance program.

• Lower costs by eliminating unnecessary maintenance or overhauls.

• Minimize frequency of overhauls.

• Reduced probability of sudden equipment failures

• Increased component reliability.

Disadvantages

• Can have significant start-up cost, training, equipment, etc.

• Savings potential not readily seen by management.

PLANNED PREVENTIVE MAINTENANCE 

Planned Preventive Maintenance ('PPM') or more usual just simple Planned

Maintenance (PM) or Scheduled Maintenance is any variety of scheduled maintenance to an

object or item of equipment. Specifically, Planned Maintenance is a scheduled service visit

carried out by a competent and suitable agent, to ensure that an item of equipment is operating

correctly and to therefore avoid any unscheduled breakdown and downtime.

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Together with Condition Based Maintenance, Planned maintenance comprises preventive

maintenance, in which the maintenance event is preplanned, and all future maintenance is pre-

programmed. Planned maintenance is created for every item separately according to

manufacturer’s recommendation or legislation. Plan can be based on equipment running hours,

date based, or for vehicles distance travelled. A good example of a planned maintenance program

is car maintenance, where time and distance determine fluid change requirements. A good

example of Condition Based Maintenance is the oil pressure warning light that provides

notification that you should stop the vehicle because failure will occur because engine

lubrication has stopped.

Planned maintenance has some advantages over Condition Based Maintenance such as:

• easier planning of maintenance and ordering spares,

• costs are distributed more evenly,

• no initial costs for instruments for supervision of equipment.

Disadvantages are:

• less reliable than equipment with fault reporting associated with CBM

• more expensive due to more frequent parts change.

• requires training investment and ongoing labour costs

Parts that have scheduled maintenance at fixed intervals, usually due to wearout or a fixed shelf

life, are sometimes known as time-change interval, or TCI items

Preventive Maintenance (Time-Based Maintenance)

Basic philosophy

• Schedule maintenance activities at predetermined time intervals.

• Repair or replace damaged equipment before obvious problems occur

This philosophy entails the scheduling of maintenance activities at predetermined time intervals,

where damaged equipment is repaired or replaced before obvious problems occur.. The

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advantages of this approach are that it works well for equipment that does not run continuously,

and with personnel who have enough knowledge, skills, and time to perform the preventive

maintenance work.

Predictive Maintenance (Condition-Based Maintenance)

Basic philosophy

• Schedule maintenance activities when mechanical or operational conditions warrant.

• Repair or replace damaged equipment before obvious problems occur.

This philosophy consists of scheduling maintenance activities only if and when mechanical or

operational conditions warrant-by periodically monitoring the machinery for excessive vibration,

temperature and/or lubrication degradation, or by observing any other unhealthy trends that

occur over time. When the condition gets to a predetermined unacceptable level, the equipment

is shut down to repair or replace damaged components so as to prevent a more costly failure

from occurring. In other words, “Don’t fix what is not broke.” Studies have shown that when it is

done correctly, the costs to operate in this fashion are about $9 per hp per year. Advantages of

this approach are that it works very well if personnel have adequate knowledge, skills, and time

to perform the predictive maintenance work, and that it allows equipment repairs to be scheduled

in an orderly fashion. It also provides some lead-time to purchase materials for the necessary

repairs, reducing the need for a high parts inventory. Since maintenance work is only performed

when it is needed, there is likely to be an increase in production capacity.

LUBRICATION

Lubrication is the process, or technique employed to reduce wear of one or both surfaces

in close proximity, and moving relative to each other, by interposing a substance called lubricant

between the surfaces to carry or to help carry the load (pressure generated) between the opposing

surfaces. The interposed lubricant film can be a solid, (e.g. graphite, MoS2) a solid/liquid

dispersion, a liquid, a liquid-liquid dispersion (a grease) or, exceptionally, a gas.

In the most common cases the applied load is carried by pressure generated within the

fluid due to the frictional viscous resistance to motion of the lubricating fluid between the

surfaces.

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Lubrication can also describe the phenomenon such reduction of wear occurs without

human intervention (hydroplaning on a road).

The science of friction, lubrication and wear is called tribology.

The regimes of lubrication

As the load increases on the contacting surfaces three distinct situations can be observed with

respect to the mode of lubrication, which are called regimes of lubrication:

Fluid film lubrication is the lubrication regime in which through viscous forces the load is fully

supported by the lubricant within the space or gap between the parts in motion relative to one

another (the lubricated conjunction) and solid–solid contact is avoided.

Hydrostatic lubrication is when an external pressure is applied to the lubricant in the

bearing, to maintain the fluid lubricant film where it would otherwise be squeezed out.

Hydrodynamic lubrication is where the motion of the contacting surfaces, and the exact

design of the bearing is used to pump lubricant around the bearing to maintain the

lubricating film. This design of bearing may wear when started, stopped or reversed, as

the lubricant film breaks down.

Elastohydrodynamic lubrication: The opposing surfaces are separated, but there occurs

some interaction between the raised solid features called asperities, and there is an elastic

deformation on the contacting surface enlarging the load-bearing area whereby the

viscous resistance of the lubricant becomes capable of supporting the load.

Boundary lubrication (also called boundary film lubrication): The bodies come into

closer contact at their asperities; the heat developed by the local pressures causes a

condition which is called stick-slip and some asperities break off. At the elevated

temperature and pressure conditions chemically reactive constituents of the lubricant

react with the contact surface forming a highly resistant tenacious layer, or film on the

moving solid surfaces (boundary film) which is capable of supporting the load and major

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wear or breakdown is avoided. Boundary lubrication is also defined as that regime in

which the load is carried by the surface asperities rather than by the lubricant.

Besides supporting the load the lubricant may have to perform other functions as well, for

instance it may cool the contact areas and remove wear products. While carrying out these

functions the lubricant is constantly replaced from the contact areas either by the relative

movement (hydrodynamics) or by externally induced forces.

Lubrication is required for correct operation of mechanical systems pistons, pumps, cams,

bearings, turbines, cutting tools etc. where without lubrication the pressure between the surfaces

in close proximity would generate enough heat for rapid surface damage which in a coarsened

condition may literally weld the surfaces together, causing seizure.

In some applications, such as piston engines, the film between the piston and the cylinder wall

also seals the combustion chamber, preventing combustion gases from escaping into the

crankcase.

If rolling bearings are to operate reliably they must be adequately lubricated to prevent

direct metal-to-metal contact between the rolling elements, raceways and cages. The lubricant

also inhibits wear and protects the bearing surfaces against corrosion. The choice of a suitable

lubricant and method of lubrication for each individual bearing application is therefore

important, as is correct maintenance.

A wide selection of greases and oils is available for the lubrication of rolling bearings and there

are also solid lubricants, e.g. for extreme temperature conditions. The actual choice of a lubricant

depends primarily on the operating conditions, i.e. the temperature range and speeds as well as

the influence of the surroundings. The most favourable operating temperatures will be obtained

when the minimum amount of lubricant needed for reliable bearing lubrication is provided.

However, when the lubricant has additional functions, such as sealing or the removal of heat,

additional amounts of lubricant may be required. The lubricant in a bearing arrangement

gradually loses its lubricating properties as a result of mechanical work, ageing and the build-up

of contamination. It is therefore necessary for grease to be replenished or renewed and for oil to

be filtered and changed at regular intervals. The information and recommendations in this section

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relate to bearings without integral seals or shields. SKF bearings and bearing units with integral

seals and shields on both sides are supplied greased. Information about the greases used by SKF

as standard for these products can be found in the relevant product sections together with a brief

description of the performance data.

Methods of oil lubrication

Oil bath

The simplest method of oil lubrication is the oil bath (fig.1). The oil, which is picked up by the

rotating components of the bearing, is distributed within the bearing and then flows back to the

oil bath. The oil level should be such that it almost reaches the centre of the lowest rolling

element when the bearing is stationary. The use of oil levellers such as the SKF LAHD 500 is

recommended to provide the correct oil level. When operating at high speed the oil level can

drop significantly and the housing can become overfilled by the oil leveller, under these

conditions, please consult the SKF application engineering service

fig 1

Oil pick-up ring

For bearing applications where speeds and operating temperature are such that oil lubrication is

necessary and high reliability is required, the oil pick-up ring lubrication method is

recommended (fig.2). The pick-up ring serves to bring about oil circulation. The ring hangs

loosely on a sleeve on the shaft on one side of the bearing and dips into the oil in the lower half

of the housing. As the shaft rotates, the ring follows and transports oil from the bottom to a

collecting trough. The oil then flows through the bearing back into the reservoir at the bottom.

SKF plummer block housings in the SONL series are designed for the oil pick-up ring

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lubrication method. For additional information please consult the SKF application engineering

service.

fig 2

Circulating oil

Operation at high speeds will cause the operating temperature to increase and will accelerate

ageing of the oil. To avoid frequent oil changes and to achieve a fully flooded condition, the

circulating oil lubrication method is generally preferred (fig.3). Circulation is usually produced

with the aid of a pump. After the oil has passed through the bearing, it generally settles in a tank

where it is filtered and, if required, cooled before being returned to the bearing. Proper filtering

leads to high values for the factor ηc and thus to long bearing service life, see section SKF rating

life. 

fig 3

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Oil jet

For very high-speed operation a sufficient but not excessive amount of oil must be supplied to

the bearing to provide adequate lubrication, without increasing the operating temperature more

than necessary. One particularly efficient method of achieving this is the oil jet method (fig.4)

where a jet of oil under high pressure is directed at the side of the bearing. The velocity of the oil

jet must be high enough (at least 15 m/s) to penetrate the turbulence surrounding the rotating

bearing.

fig 4

Oil mist

Oil mist lubrication has not been recommended for some time due to possible negative

environmental effects.

A new generation of oil mist generators permits to produce oil mist with 5 ppm oil. New designs

of special seals also limit the amount of stray mist to a minimum. In case synthetic non-toxic oil

is used, the environmental effects are even further reduced. Oli mist lubrication today is used in

very specific applications, like the petroleum industry.

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TOTAL PRODUCTIVE MAINTANENCE

Total productive maintenance (TPM) originated in Japan in 1971 as a method for

improved machine availability through better utilization of maintenance and production

resources.

TPM is a critical adjunct to lean manufacturing. If machine uptime is not predictable and

if process capability is not sustained, the process must keep extra stocks to buffer against this

uncertainty and flow through the process will be interrupted. Unreliable uptime is caused by

breakdowns or badly performed maintenance. Correct maintenance will allow uptime to improve

and speed production through a given area allowing a machine to run at its designed capacity of

production.

One way to think of TPM is "deterioration prevention": deterioration is what happens

naturally to anything that is not "taken care of". For this reason many people refer to TPM as

"total productive manufacturing" or "total process management". TPM is a proactive approach

that essentially aims to identify issues as soon as possible and plan to prevent any issues before

occurrence. One motto is "zero error, zero work-related accident, and zero loss"

TPM is a management process developed for improving productivity by making

processes more reliable and less wasteful.TPM is an extension of TQM(Total Quality

Management). The objective of TPM is to maintain the plant or equipment in good condition

without interfering with the daily process. To achieve this objective, preventive and predictive

maintenance is required. By following the philosophy of TPM we can minimize the unexpected

failure of the equipment.

To implement TPM the production unit and maintenance unit should work jointly.

Original goal of total productive management:

“Continuously improve all operational conditions, within a production system; by stimulating

the daily awareness of all employees” (by Seiichi Nakajima, Japan, JIPM)

TPM focuses primarily on manufacturing (although its benefits are applicable to virtually

any "process") and is the first methodology Toyota used to improve its global position (1950s).

After TPM, the focus was stretched, and also suppliers and customers were involved (Supply

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Chain), this next methodology was called lean manufacturing. This sheet gives an overview of

TPM in its original form.

An accurate and practical implementation of TPM, will increase productivity within the total

organization, where:

a clear business culture is designed to continuously improve the efficiency of the total

production system.

a standardized and systematic approach is used, where all losses are prevented and/or

known.

all departments, influencing productivity, will be involved to move from a reactive- to a

predictive mindset.

a transparent multidisciplinary organization in reaching zero losses.

steps are taken as a journey, not as a quick menu.

Finally TPM will provide practical and transparent ingredients to reach operational excellence.

PM has basically 3 goals - Zero Product Defects, Zero Equipment Unplanned Failures

and Zero Accidents. It sets out to achieve these goals by Gap Analysis of previous historical

records of Product Defects, Equipment Failures and Accidents. Then through a clear

understanding of this Gap Analysis (Fishbone Cause-Effect Analysis, Why-Why Cause-Effect

Analysis, and P-M Analysis) plan a physical investigation to discover new latent fuguai (slight

deterioration) during the first step in TPM Autonomous Maintenance called "Initial Cleaning".

.

TPM identifies the 7 losses (types of waste) (muda), namely set-up and initial adjustment

time, equipment breakdown time, idling and minor losses, speed (cycle time) losses, start-up

quality losses, and in process quality losses, and then works systematically to eliminate them by

making improvements (kaizen). TPM has 8 pillars of activity,[2] each being set to achieve a

“zero” target. These 8 pillars are the following: focussed improvement (Kobetsu Kaizen);

autonomous maintenance (Jishu Hozen); planned maintenance; training and education; early-

phase management; quality maintenance (Hinshitsu Hozen); office TPM; and safety, health, and

environment. Few organisation also add Pillars according to their Work Place like: Tools

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Management; Information Technology & more. The Base for the TPM Activity is 5S; Seiri

(Sorting out the required or not required items); Seition (Systematic Arrangement of the required

items); Seiso (Cleaniness); Seiketsu (Standardisation); Shitsuke (Self Discipline).

The Pillars & their details

a) Efficient Equipment Utilisation

b) Efficient Worker Utilisation

c) Efficient Material & Energy Utilisation

1. Focussed improvement (Kobetsu Kaizen) - Continuously even small steps of

improvement.

2. Planned Maintenance - It focusses on Increasing Availability of Equipments & reducing

Breakdown of Machines.

3. Initial Control - To establish the system to launch the production of new product & new

equipment in a minimum run up time.

4. Education & Training - Formation of Autonomous workers who have skill & technique

for autonomous maintenance.

5. Autonomous Maintenance (Jishu Hozen) - It means "Maintaining one's equipment by

oneself". There are 7 Steps in & Activities of Jishu Hozen.

6. Quality Maintenance (Hinshitsu Hozen) - Quality Maintenance is establishment of

machine conditions that will not allow the occurrence of defects & control of such

conditions is required to sustain Zero Defect.

7. Office TPM - To make an efficient working office that eliminate losses.

8. Safety, Hygiene & Environment - The main role of SHE (Safety, Hygiene &

Environment) is to create Safe & healthy work place where accidents do not occur,

uncover & improve hazardous areas & do activities that preserve environment.

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Other Pillars Like: Tools Management - To increase the availability of Equipment by reducing

Tool Resetting Time, To reduce Tool Consumption Cost & to increase the tool life.

TPM success measurement - A set of performance metrics which is considered to fit well

in a lean manufacturing/TPM environment is overall equipment effectiveness, or OEE. For

advanced TPM world class practitioners, the OEE cannot be converted to costs using Target

Costing Management (TCM) OEE measurements are used as a guide to the potential

improvement that can be made to equipment and by identifying which of the 6 losses is the

greater, then the techniques applicable to that type of loss. Consistent application of the

applicable improvement techniques to the sources of major losses will positively impact the

performance of that equipment.

Using a criticality analysis across the factory should identify which equipments should be

improved first, also to gain the quickest overall factory performance.

The use of Cost Deployment is quite rare, but can be very useful in identifying the

priority for selective TPM deployment.

REPAIRABLE

Repairable parts are parts that are deemed worthy of repair, usually by virtue of economic

consideration of their repair cost.

Rather than bear the cost of completely replacing a finished product, repairable typically

are designed to enable more affordable maintenance by being more modular.

This allows components to be more easily removed, repaired, and replaced, enabling

cheaper replacement.

Spare parts that are needed to support condemnation of repairable parts are known as

replenishment spares.

A rotable pool is a pool of repairable spare parts inventory set aside to allow for multiple

repairs to be accomplished simultaneously.

This can be used to minimize stockout conditions for repairable items.

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REPAIR CYCLE

From the perspective of logistics, a model of the life cycle of parts in a supply chain can

be developed.

This model, called the repair cycle, consists of functioning parts in use by equipment

operators, and the entire sequence of suppliers or repair providers that replenish

functional part inventories, either by production or repair, when they have failed.

Ultimately, this sequence ends with the manufacturer.

This type of model allows demands on a supply system to ultimately be traced to their

operational reliability, allowing for analysis of the dynamics of the supply system, in

particular, spare parts.

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UNIT III

CONDITION MONITORING

Condition Monitoring – Cost comparison with and without CM – On-load testing and off-load

testing – Methods and instruments for CM – Temperature sensitive tapes – Pistol thermometers –

wear-debris analysis

CONDITION MONITORING

Condition monitoring is the process of monitoring a parameter of condition in machinery,

such that a significant change is indicative of a developing failure.

It is a major component of predictive maintenance. The use of conditional monitoring

allows maintenance to be scheduled, or other actions to be taken to avoid the

consequences of failure, before the failure occurs.

Nevertheless, a deviation from a reference value (e.g. temperature or vibration behaviour)

must occur to identify impeding damages

Predictive Maintenance does not predict failure.

Machines with defects are more at risk of failure than defect free machines. Once a defect

has been identified, the failure process has already commenced and CM systems can only

measure the deterioration of the condition.

Intervention in the early stages of deterioration is usually much more cost effective than

allowing the machinery to fail. Condition monitoring has a unique benefit in that the

actual load, and subsequent heat dissipation that represents normal service can be seen

and conditions that would shorten normal lifespan can be addressed before repeated

failures occur.

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Serviceable machinery includes rotating equipment and stationary plant such as boilers

and heat exchangers.

METHODS OF CM

Screen monitoring records video or static images detailing the contents, or screen capture,

of the entire [video display] or the content of the screen activity within a particular

program or computer application. Monitoring tools may collect real time video,

accelerated or [time-lapse] video or screen shots, or may take video or still image

captures at regular intervals (e.g., once every 4 minutes). They may collect images

constantly or only collect information while the user is interacting with the equipment

(e.g., capturing screens when the mouse or keyboard is active).

Data monitoring tracks the content of and changes to files stored on the local [hard drive]

or in the user's "private" network share.

Keystroke monitoring (e.g., number of keystrokes per minute) may track the performance

of keyboard-intensive work such as word processing or data entry. Keystroke logging

captures all keyboard input to enable the employer to monitor anything typed into the

monitored machine.

Idle time monitoring keeps track of time when the employee is away from the computer

or the computer is not being actively used.

BENEFITS

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Screen monitoring records video or static images detailing the contents, or screen capture,

of the entire [video display] or the content of the screen activity within a particular

program or computer application.

Monitoring tools may collect real time video, accelerated or [time-lapse] video or screen

shots, or may take video or still image captures at regular intervals (e.g., once every 4

minutes).

They may collect images constantly or only collect information while the user is

interacting with the equipment (e.g., capturing screens when the mouse or keyboard is

active).

Data monitoring tracks the content of and changes to files stored on the local [hard drive]

or in the user's "private" network share.

Keystroke monitoring (e.g., number of keystrokes per minute) may track the performance

of keyboard-intensive work such as word processing or data entry. Keystroke logging

captures all keyboard input to enable the employer to monitor anything typed into the

monitored machine.

Idle time monitoring keeps track of time when the employee is away from the computer

or the computer is not being actively used .

LOAD TESTING

Load testing is the process of putting demand on a system or device and measuring its

response.

Load testing is performed to determine a system’s behavior under both normal and

anticipated peak load conditions.

29

It helps to identify the maximum operating capacity of an application as well as any

bottlenecks and determine which element is causing degradation.

When the load placed on the system is raised beyond normal usage patterns, in order to

test the system's response at unusually high or peak loads, it is known as stress testing.

The load is usually so great that error conditions are the expected result, although no clear

boundary exists when an activity ceases to be a load test and becomes a stress test.

There is little agreement on what the specific goals of load testing are.

The term is often used synonymously with concurrency testing, software performance

testing, reliability testing, and volume testing.

Load testing is a type of non-functional testing.

TEMPERATURE-SENSITIVE TAPE:

 It obtains only your body surface temperature and does not indicate the core temperature.

The tape is applied to the skin, forehead and abdomen. Inside the tape is liquid crystals that

change colour according to temperature.

INFRARED THERMOMETER:

An infrared thermometer is a thermometer which infers temperature from a portion of

the thermal radiation sometimes called blackbody radiation emitted by the object being

measured. They are sometimes called laser thermometers if a laser is used to help aim the

thermometer, or non-contact thermometers to describe the device's ability to measure

temperature from a distance. By knowing the amount of infrared energy emitted by the object

and its emissivity, the object's temperature can often be determined. Infrared thermometers are a

subset of devices known as "thermal radiation thermometers".

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Sometimes, especially near ambient temperatures, false readings will be obtained indicating

incorrect temperature. This is most often due to other thermal radiation reflected from the object

being measured, but having its source elsewhere, like a hotter wall or other object nearby - even

the person holding the thermometer can be an error source in some cases. It can also be due to an

incorrect emissivity on the emissivity control or a combination of the two possibilities.

The most basic design consists of a lens to focus the infrared thermal radiation on to a detector,

which converts the radiant power to an electrical signal that can be displayed in units of

temperature after being compensated for ambient temperature. This configuration facilitates

temperature measurement from a distance without contact with the object to be measured. As

such, the infrared thermometer is useful for measuring temperature under circumstances

where thermocouples or other probe type sensors cannot be used or do not produce accurate data

for a variety of reasons.

Some typical circumstances are where the object to be measured is moving; where the object is

surrounded by an electromagnetic field, as in induction heating; where the object is contained in

a vacuum or other controlled atmosphere; or in applications where a fast response is required, an

accurate surface temperature is desired or the object temperature is above the recommended use

point of a contact sensors, or contact with a sensor would mar the object or the sensor, or

introduce a significant temperature gradient on the object's surface.

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Infrared thermometers can be used to serve a wide variety of temperature monitoring

functions. A few examples provided to this article include:

Detecting clouds for remote telescope operation

Checking mechanical equipment or electrical circuit breaker boxes or outlets for hot spots

Checking heater or oven temperature, for calibration and control purposes

Detecting hot spots / performing diagnostics in electrical circuit board manufacturing

Checking for hot spots in fire fighting situations

Monitoring materials in process of heating and cooling, for research and development or

manufacturing quality control situations

There are many varieties of infrared temperature sensing devices available today, including

configurations designed for flexible and portable handheld use, as well many designed for

mounting in a fixed position to serve a dedicated purpose for long periods.

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Specifications of portable handheld sensors available to the home user will include ratings of

temperature accuracy (usually with measurement uncertainty of ±2 °C/±4 °F) and other

parameters.

The distance-to-spot ratio (D:S) is the ratio of the distance to the object and the diameter of the

temperature measurement area. For instance if the D:S ratio is 12:1, measurement of an object 12

inches (30 cm) away will average the temperature over a 1-inch-diameter (25 mm) area. The

sensor may have an adjustable emissivity setting, which can be set to measure the temperature of

reflective (shiny) and non-reflective surfaces.

A non-adjustable thermometer sometimes can be used to measure the temperature of a shiny

surface by applying a non-shiny paint or tape to the surface, if the allowed measurement error is

acceptable.

The most common infrared thermometers are the:

Spot Infrared Thermometer or Infrared Pyrometer, which measures the temperature

at a spot on a surface (actually a relatively small area determined by the D:S ratio).

Related equipment, although not strictly thermometers, includes:

Infrared Scanning Systems scan a larger area, typically by using what is essentially a

spot thermometer pointed at a rotating mirror. These devices are widely used in

manufacturing involving conveyors or "web" processes, such as large sheets of glass or

metal exiting an oven, fabric and paper, or continuous piles of material along a conveyor

belt.

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34

WEAR DEBRIS ANALYSIS

Using a Scanning Electron Microscope of a carefully taken sample of debris suspended in

lubricating oil (taken from filters or magnetic chip detectors).

Instruments then reveal the elements contained their proportions, size and morphology.

Using this method, the site, the mechanical failure mechanism and the time to eventual failure

may be determined. This is called WDA - Wear Debris Analysis

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UNIT IV

REPAIR METHODS FOR BASIC MACHINE ELEMENTS

Repair methods for beds, slideways, spindles, gears, lead screws and bearings – Failure

analysis – Failures and their development – Logical fault location methods – Sequential

fault location.

SPINDLE REPAIR - How to Properly Repair Precision Spindles. 

Did your spindle fail prematurely after having it repaired? A major contributor to

premature spindle failure is caused directly by the spindle repair process itself.

It is important that the spindle repair facility you choose to repair your Spindle, understands and

recognizes the need for maintaining exacting tolerances, attention to detail and the necessity for

controlling the proper cleanliness levels for all facets of the spindle repair process.

Especially critical is the prepping and Ultrasonic Cleaning of all components utilizing 3

micron “Absolute” filtration for all of the Cleaning Solvents, blowing off of parts with

Compressed Air that is dried to a minimum dew point of -40 degree F and filtered with .08

Micron “Absolute Filtration” just prior to assembly. The assembly must be done in a Certified

“Class 10,000 Clean Room” and when practical, in a “Certified Class 1,000 Laminar Flow

Bench”.

36

This is particularly important for “Open” bearings where they have been Grease Packed

for life. If the precision “ABEC 7 or 9” bearings are exposed to dust and dirt particles that are 3 –

5 microns in size and considering the human eye with 20/20 vision can only see 40 micron size

particles, you cannot see the dirt that will damage your bearings. This invisible dirt is always

present and can dramatically reduce the overall Service Life of a bearing and may cause

premature failure of your Spindle.

Even when dealing with bearings that are “Air-Oil” or "Air Oil Mist" lubricated, it is still

important to keep the whole process “Clean”, as the bearings can ingest dirt and dust during

handling and assembly and ultimately sustain undetected damage during the initial startup of the

Spindle. The bearings won’t necessarily fail immediately, but can and will gradually deteriorate

over a period of time. This is known as “McPherson’s Curve”, the chain reaction of wear. If

bearings start out clean and are kept clean, providing the lubricants and the compressed air

delivering the lubrication, where applicable, is “Clean and Dry”, the bearings theoretically, can

last forever, unless “Crashed” or mistreated.

If your spindle repair source does not have the type of facility that incorporates and

“maintains” the Cleanliness levels that are absolutely imperative to the long term health of your

Spindle, you should look elsewhere. You are paying for that level of service and should demand

that anyone repairing your production machine Spindles comply with the cleanliness levels

needed. If this process control is not embraced and adhered to, ultimately, you could receive a

Spindle back from repair that will fail prematurely. How important is it to your manufacturing

facility and your production schedule that your Spindles run and produce quality parts for an

extended period of time? What is the cost of a “Premature” Spindle failure or “Downtime” to

your business?

You need to ask questions about the spindle repair process and the level of expertise for

the personnel repairing your precision Spindle. The Spindle is the “Heart” of your production

machinery.

Atlanta Precision Spindle’s key people have spent years doing the right things. We have

set many of the industry standards for “Clean Dry Oil and Clean Dry Compressed Air” as it

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relates to Spindles. We filter our cleaning solvents that process all of the various components

with 3 micron absolute filtration prior to the final assembly. All of the assembly is done in a

“Certified Class 10,000 Clean Room”, and whenever practical, in a “Certified Class 100 Laminar

Flow Bench”. If Spindles require Air Oil or Air Oil Mist Lubrication, we use only “Purified

Lube Oil” that meet or exceed an ISO Cleanliness level of 14/13/10. You can be assured that

when your Spindle leaves our facility, you have not purchased a dirty uncontrolled Repair

process or dirty wet lube oil or compressed air. We do it right!

Our Written Repair Certification includes running your Spindle at its maximum rated

speed and also at the speed where you historically run the Spindle. Our detailed Spectrum

Analysis is performed utilizing the latest equipment and technology from Schenck-Trebel, the

world leader in balancing and diagnostic testing equipment for rotating assemblies. We are

continually looking for changes and advancements in Spindle testing technology, so those

advancements can be passed along to you. “We want to be Partners in your success”.

FAILURE ANALYSIS

Failure analysis is the process of collecting and analyzing data to determine the cause of

a failure. It is an important discipline in many branches of manufacturing industry, such as the

electronics industry, where it is a vital tool used in the development of new products and for the

improvement of existing products. It relies on collecting failed components for subsequent

examination of the cause or causes of failure using a wide array of methods,

especially microscopy and spectroscopy. The NDT or non-destructive testing methods are

valuable because the failed products are unaffected by analysis, so inspection always starts using

these methods.

A failure analysis engineer often plays a lead role in the analysis of failures, whether a

component or product fails in service or if failure occurs in manufacturing or during production

processing. In any case, one must determine the cause of failure to prevent future occurrence,

and/or to improve the performance of the device, component or structure

Method of Analysis

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The failure analysis of many different products involves the use of the following tools and

techniques:

Microscopes

Optical microscope

Liquid crystal

Scanning acoustic microscope (SAM)

Scanning acoustic tomography (SCAT)

Atomic force microscope (AFM)

Stereomicroscope

Photo emission microscope (PEM)

X-ray microscope

Infra-red microscope

Scanning SQUID microscope

Sample preparation

Jet-etcher

Plasma etcher

Back side thinning tools

Mechanical back-side thinning

Laser chemical back-side etching

Spectroscopic analysis

Transmission line pulse spectroscopy (TLPS)

Auger electron spectroscopy

39

Deep-level transient spectroscopy (DLTS)

Device modification

Focused ion beam etching (FIB)

Surface analysis

Dye penetrant inspection

Other Surface analysis tools

Scanning electron microscopy

Scanning electron microscope (SEM)

Electron beam induced current (EBIC) in SEM

Charge-induced voltage alteration (CIVA) in SEM

Voltage contrast in SEM

Electron backscatter diffraction (EBSD) in SEM

Energy-dispersive X-ray spectroscopy (EDS) in SEM

Transmission electron microscope (TEM)

Laser signal injection microscopy (LSIM)

Photo carrier stimulation

Static

Optical beam induced current (OBIC)

Light-induced voltage alteration (LIVA)

Dynamic

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Laser-assisted device alteration (LADA)

Thermal laser stimulation (TLS)

Static

Optical-beam-induced resistance change (OBIRCH)

Thermally induced voltage alteration (TIVA)

External induced voltage alteration (XIVA)

Seebeck effect imaging (SEI)

Dynamic

Soft defect localization (SDL)

Semiconductor probing

Mechanical probe station

Electron beam prober

Laser voltage prober

Time-resolved photon emission prober (TRPE)

FAULT DIAGNOSIS

Basic Concepts

A unit under test (UUT) fails when its observed behaviour is different from its expected

behaviour. Diagnosis consists of locating the physical fault(s) in a structural model of the UUT.

The degree of accuracy to which faults can be located is called diagnostic

resolution. Functionally equivalent faults (FEF) cannot be distinguished. The partition of all

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faults into distinct subsets of FEF defines the maximal fault resolution. A test that achieves the

maximal fault resolution is said to be a complete fault-location test.

Repairing the UUT often consists of substituting one of its replaceable units (RU)

referred as a faulty RU, rather than in an accurate identification of the real fault inside an RU.

We characterize this process by RU resolution. Suppose that the results of the test do not allow to

distinguish between two suspected RUs U1 and U2. We could replace now one of these RUs, say

U1 with a good RU, and return to the test experiment. If the new results are correct, the faulty

RU was the replaced one; otherwise, it is the remaining one U2. This type of procedure we

call sequential diagnosis procedure.

The diagnosis process is often hierarchical, carried out as a top-down process (with a

system operating in the field) or bottom-up process (during the fabrication of the system).

In the top-down approach (system   boards   ICs) first-level diagnosis may deal with

"large" RUs like boards called also field-replaceable units. The faulty board is then tested in a

maintenance centre to locate the faulty component (IC) on the board. Accurate location of faults

inside a faulty IC may be also useful for improving its manufacturing process. 

In the bottom-up approach (ICs  boards  system) a higher level is assembled only

from components already tested at a lower level. This is done to minimize the cost of diagnosis

and repair, which increases significantly with the level at which the faults are detected.

The rule of 10: if it costs $1 to test an IC, the cost of locating the same defective IC when

mounted on a board and of repairing the board is about $10; when the defective board is plugged

into a system, the cost of finding the fault and repairing the system is $100.

In manufacturing, the most likely faults are fabrication errors affecting the interconnections

between components; in the field the most likely faults are physical failures internal to

components (because every UUT has been successfully tested in the past). Knowing the most

likely class of faults helps in fault location.

 

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COMBINATIONAL FAULT DIAGNOSIS METHODS

This approach does most of the work before the testing experiment. It uses fault simulation to

determine the possible responses to a given test in the presence of faults. The database

constructed in this step is called a fault table or a fault dictionary. To locate faults, one tries to

match the actual results of test experiments with one of the precomputed expected results stored

in the database. The result of the test experiment represents a combination of effects of the fault

to each test pattern. That's why we call this approach combinational fault diagnosis method. If

this look-up process is successful, the fault table (dictionary) indicates the corresponding fault(s).

On the applet, select Fault Diagnosis Mode, after that a circuit layout, insert needed

vectors and simulate faults. A fault table will be produced.

1. Fault tables

2. Fault dictionaries

3. Minimization of diagnostic data

4. Fault location by structural analysis

1. Fault Table

In general, a fault table is a matrix   where columns Fj represent faults, rows

Ti represent test patterns, and aij = 1 if the test pattern Ti detects the fault Fj, otherwise if the test

pattern Ti does not detect the fault Fj, aij = 0. 

Denote the actual result of a given test pattern by 1 if it differs from the precomputed expected

one, otherwise denote it by 0. The result of a test experiment is represented by a vector   

where ei = 1 if the actual result of the test patterns does not match with the expected result,

otherwise ei = 0. Each column vector fj corresponding to a fault Fj represents a possible result of

the test experiment in the case of the fault Fj. 

Three cases are now possible depending on the quality of the test patterns used for carrying out

the test experiment:

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1. The test result E matches with a single column vector fj in FT. This result corresponds to

the case where a single fault Fj has been located. In other words, the maximum diagnostic

resolution has been obtained.

2. The test result E matches with a subset of column vectors {fi, fj … fk} in FT. This result

corresponds to the case where a subset of indistinguishable faults {Fi, Fj … Fk} has been

located.

3. No match for E with column vectors in FT is obtained. This result corresponds to the case

where the given set of vectors does not allow to carry out fault diagnosis. The set of faults

described in the fault table must be incomplete (in other words, the real existing fault is

missing in the fault list considered in FT).

Example:

In the example the results of three test experiments E1, E2, E3 are demonstrated. E1 corresponds to

the first case where a single fault is located, E2 corresponds to the second case where a subset of

two indistinguishable faults is located, and E3 corresponds to the third case where no fault can be

located because of the mismatch of E3 with the column vectors in the fault table.

2. Fault Dictionary

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Fault dictionaries (FD) contain the same data as the fault tables with the difference that the data

is reorganized. In FD a mapping between the potential results of test experiments and the faults

is represented in a more compressed and ordered form. For example, the column bit vectors can

be represented by ordered decimal codes (see the example) or by some kind of compressed

signature.

Example:

 

3. Minimization of Diagnostic Data

To reduce large computational effort involved in building a fault dictionary, in fault simulation

the detected faults are dropped from the set of simulated faults. Hence, all the faults detected for

the first time by the same vector will produce the same column vector (signature) in the fault

table, and will be included in the same equivalence class of faults. In this case the testing

experiment can stop after the first failing test, because the information provided by the following

tests is not used. Such a testing experiment achieves a lower diagnostic resolution. A trade off

between computing time and diagnostic resolution can be achieved by dropping faults after k>1

detections.

Example:

In the fault table produced by fault simulation with fault dropping, only 19 faults need to be

simulated compared to the case of 42 faults when simulation without fault dropping is carried out

(the simulated faults in the fault table are shown in shadowed boxes). As the result of the fault

dropping, however, the following faults remain not distinguishable: {F2, F3},{F1, F4},{F2, F6}.

45

 

4. Fault Location by Structural Analysis 

Assume a single fault in the circuit. Then there should exist a path from the site of the fault to

each of the outputs where errors have been detected. Hence the fault site should belong to the

intersection of cones of all failing outputs. A simple structural analysis can help to find faults

that can explain all the observed errors.

SEQUENTIAL FAULT DIAGNOSIS METHODS

In sequential fault diagnosis the process of fault location is carried out step by step, where

each step depends on the result of the diagnostic experiment at the previous step. Such a test

experiment is called adaptive testing. Sequential experiments can be carried out either by

observing only output responses of the UUT or by pinpointing by a special probe also internal

control points of the UUT (guided probing). Sequential diagnosis procedure can be

1. Fault location by edge-pin testing

2. Generating tests to distinguish faults

3. Guided-probe testing

4. Fault location by UUT reduction

1. Fault Location by Edge-Pin Testing

In fault diagnosis test patterns are applied to the UUT step by step. In each step, only output

signals at edge-pins of the UUT are observed and their values are compared to the expected ones.

The next test pattern to be applied in adaptive testing depends on the result of the previous step.

The diagnostic tree of this process consists of the fault nodes FN (rectangles) and test nodes TN

46

(circles). A FN is labeled by a set of not yet distinguished faults. The starting fault node is

labeled by the set of all faults. To each FN k a TN is linked labeled by a test pattern Tk to be

applied as the next. Every test pattern distinguishes between the faults it detects and the ones it

does not. The task of the test pattern Tk is to divide the faults in FN k into two groups - detected

and not detected by Tk faults. Each test node has two outgoing edges corresponding to the results

of the experiment of this test pattern. The results are indicated as passed (P) or failed (F). The set

of faults shown in a current fault node (rectangle) are equivalent (not distinguished) under the

currently applied test set.

Example:

The diagnostic tree in the Figure below corresponds to the example considered in 3.2.1. We can

see that most of the faults are uniquely identified, two faults F1,F4 remain indistinguishable. Not

all test patterns used in the fault table are needed. Different faults need for identifying test

sequences with different lengths. The shortest test contains two patterns the longest four patterns.

Rather than applying the entire test sequence in a fixed order as in combinational fault diagnosis,

adaptive testing determines the next vector to be applied based on the results obtained by the

preceding vectors. In our example, if T1 fails, the possible faults are {F2,F3}. At this point

applying T2 would be wasteful, because T2 does not distinguish among these faults. The use of

adaptive testing may substantially decrease the average number of tests required to locate a fault.

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 2. Generating Tests to Distinguish Faults

To improve the fault resolution of a given test set T, it is necessary to generate tests to

distinguish among faults equivalent under T.

Consider the problem of generating a test to distinguish between faults F1 and F2. Such a test

must detect one of these faults but not the other, or vice versa. The following cases are possible.

1. F1 and F2 do not influence the same set of outputs. Let OUT(Fk) be the set of outputs

influenced by the fault Fk. A test should be generated for F1 using only the circuit

feeding the outputs OUT(F1), or for F2 using only the circuit feeding the

outputs OUT(F2).

2. F1 and F2 influence the same set of outputs. A test should be generated for F1 without

activating F2, or vice versa, for F2 without activating F1.

Three possibilities can be mentioned to keep a fault F2: xk e not activated, where xk denotes a

line in the circuit, and e {0,1}:

1. The value  e should be assigned to the line xk.

2. If this is not possible then the activated path from F2 should be blocked, so that the

fault F2 could not propagate and influence the activated path from F1.

3. If the 2nd case is also not possible then the values propagated from the

sites F1 and F2 and reaching the same gate G should be opposite on the inputs of G.

Example:

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1. There are two faults in the circuit: F1: x3,1 0, and F2: x4 1. The fault F1 may influence

both outputs, the fault F2 may influence only the output x8. A test pattern 0010

activatesF1 up to the both outputs, and F2 only to x8. If both outputs will be wrong, F1 is

present, and if only the output x8 will be wrong, F2 is present.

2. There are two faults in the circuit: F1: x3,2 0, and F2: x5,2 1. Both of them influence the

same output of the circuit. A test pattern 0100 activates the fault F2. The fault F1 is not

activated, because the line x3,2 has the same value as it would have had if F1 were

present.

3. There are the same two faults in the circuit: F1: x3,2 0, and F2: x5,2 1. Both of them

influence the same output of the circuit. A test pattern 0110 activates the fault F2. The

faultF1 is activated at its site but not propagated through the AND gate, because of the

value x4 = 0 at its input.

4. There are two faults in the circuit: F1: x3,1 1, and F2: x3,2 1. A test pattern 1001 consists

the value x1 1 which creates the condition where both of the faults may influence only

the same output x8. On the other hand, the test pattern 1001 activates both of the faults to

the same OR gate (i.e. none of them is blocked). However, the faults produce different

values at the inputs of the gate, hence they are distinguished. If the output value on x8 will

be 0, F1 is present. Otherwise, if the output value on x8 will be 1, either F2 is present or

none of the faults F1 and F2 are present.

3. Guided-Probe Testing

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Guided-probe testing extends edge-pin testing process by monitoring internal signals in the UUT

via a probe which is moved (usually by an operator) following the guidance provided by the test

equipment. The principle of guided-probe testing is to backtrace an error from the primary output

where it has been observed during edge-pin testing to its physical location in the UUT. Probing

is carried out step-by-step. In each step an internal signal is probed and compared to the expected

value. The next probing depends on the result of the previous step. 

A diagnostic tree can be created for the given test pattern to control the process of probing. The

tree consists of internal nodes (circles) to mark the internal lines to be probed, and of terminal

nodes (rectangles) to show the possible result of diagnosis. The results of probing are indicated

as passed (P) or failed (F).

Typical faults located are opens and defective components. An open between two points A and B

in a connection line is identified by a mismatch between the error observed at B and the correct

value measured at A. A faulty device is identified by detecting an error at one of its outputs,

while only correct values are measured at its inputs.

The most time-consuming part of guided-probe testing is moving the probe. To speed-up the

fault location process, we need to reduce the number of probed lines. A lot of methods to

minimize the number of probings are available.

Example:

Let have a test pattern 1010 applied to the inputs of the circuit. The diagnostic tree created for

this particular test pattern is shown. On the output x8 , instead of the expected value 0, an

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erroneous signal 1 is detected. By back tracing (indicated by bold arrows in the diagnostic tree)

the faulty component NOR- x5 is located.

Diagnostic tree allows to carry out optimization of the fault location procedure, for example to

generate a procedure with minimum average number of probes.

4. Fault Location by UUT Reduction

Initially the UUT is the entire circuit and the process starts when its test fails. While the failing

UUT can be partitioned, half of the UUT is disabled and the remaining half is tested. If the test

passes, the fault must be in the disabled part, which then becomes the UUT. If the test fails, the

tested part becomes the UUT.

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UNIT V

REPAIR METHODS FOR MATERIAL HANDLING EQUIPMENT

Repair methods for Material handling equipment - Equipment records –Job order

systems -Use of computers in maintenance.

MATERIAL HANDLING EQUIPMENT 

Material handling equipment is equipment that relate to the movement, storage, control

and protection of materials, goods and products throughout the process of manufacturing,

distribution, consumption and disposal. Material handling equipment is the mechanical

equipment involved in the complete system. Material handling equipment is generally separated

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into four main categories: storage and handling equipment, engineered systems, industrial trucks,

and bulk material handling.

Categories of Material Handling Equipment

 

The four main categories of material handling equipment include:

Storage

Engineered systems

Industrial trucks

Bulk material handling

Storage and Handling Equipment

 

Storage equipment is usually limited to non-automated examples, which are grouped in

with engineered systems. Storage equipment is used to hold or buffer materials during

“downtimes,” or times when they are not being transported. These periods could refer to

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temporary pauses during long-term transportation or long-term storage designed to allow the

buildup of stock. The majority of storage equipment refers to pallets, shelves or racks onto which

materials may be stacked in an orderly manner to await transportation or consumption. Many

companies have investigated increased efficiency possibilities in storage equipment by designing

proprietary packaging that allows materials or products of a certain type to conserve space while

in inventory.

 

Examples of storage and handling equipment include:

 

Racks, such as pallet racks, drive-through or drive-in racks, push-back racks, and sliding

racks

Stacking frames

Shelves, bins and drawers

Mezzanines

Engineered Systems

 

Engineered systems cover a variety of units that work cohesively to enable storage and

transportation. They are often automated. A good example of an engineered system is an

Automated Storage and Retrieval System, often abbreviated AS/RS, which is a large automated

organizational structure involving racks, aisles and shelves accessible by a “shuttle” system of

retrieval. The shuttle system is a mechanized cherry picker that can be used by a worker or can

perform fully automated functions to quickly locate a storage item’s location and quickly retrieve

it for other uses.

 

Other types of engineered systems include:

 

Conveyor systems

Robotic delivery systems

Automatic guided vehicles (AGV)

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Industrial Trucks

 

Industrial trucks refer to the different kinds of transportation items and vehicles used to

move materials and products in materials handling. These transportation devices can include

small hand-operated trucks, pallet-jacks, and various kinds of forklifts. These trucks have a

variety of characteristics to make them suitable for different operations. Some trucks have forks,

as in a forklift, or a flat surface with which to lift items, while some trucks require a separate

piece of equipment for loading. Trucks can also be manual or powered lift and operation can be

walk or ride, requiring a user to manually push them or to ride along on the truck. A stack truck

can be used to stack items, while a non-stack truck is typically used for transportation and not for

loading.

 

There are many types of industrial trucks:

* Hand trucks

* Pallet jacks

* Pallet trucks

* Walkie stackers

* Platform trucks

* Order picker

* Sideloader

Bulk Material Handling Equipment

 

Bulk material handling refers to the storing, transportation and control of materials in

loose bulk form. These materials can include food, liquid, or minerals, among others. Generally,

these pieces of equipment deal with the items in loose form, such as conveyor belts or elevators

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designed to move large quantities of material, or in packaged form, through the use of drums and

hoppers.

 

* Conveyor belts

* Stackers

* Reclaimers

* Bucket elevators

* Grain elevators

* Hoppers

* Silos

A SYSTEMATIC APPROACH TO MATERIAL HANDLING MAINTENANCE

The term material handling equipment refers to conveyors, sorters, spirals, carousels, and

a wide assortment of electrical and mechanical devices. Proper maintenance of this equipment is

essential, because it prevents the loss of business or production caused by mechanical failure.

This article introduces a systematic approach to material handling maintenance based on these

lessons, and includes important tips to prevent common material handling maintenance mistakes.

The first step in material handling equipment maintenance is to list all material handling

equipment. This step is important because it creates a starting point from which a company can

develop ways to improve its physical assets. Within manufacturing operations, the list should

include all physical assets, production equipment and processes as well as facility assets. For

large distribution centers (DCs), this should include all major areas: mobile equipment, conveyor

systems, sorter systems and facility-related assets, as well as bar code scanners, printers and

other devices that keep a DC functioning.

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Because maintenance depends on more than just knowing what equipment is in place, companies

should take into account other factors that could affect how the equipment runs while an

equipment list is being compiled. For example, equipment operating in the desert of Nevada with

blowing sand requires more maintenance than in a mild climate on the East Coast. Other factors

include terrain, border regulations and the implications of schedules, calendars, cycles and peaks.

Some questions to answer are:

* Is my facility's material handling equipment running three shifts and on weekends?

* Is it indoors or outside?

* Is there moisture or harsh operating conditions?

After the list is made, the company should evaluate the current state of maintenance,

determining its strengths and weaknesses, as well as potential results from improvement

opportunities. The next step is to develop and implement a strategic maintenance plan. This plan

must include a customized preventive maintenance (PM) program to ensure that the equipment

runs with high reliability. PM is a continuous process, the objective of which is to minimize

future maintenance problems. A PM program costs extra on the front end, but savings come

quickly. Studies have shown that operations with PM spend less for maintenance than reactive

run-to-failure operations.

The best approach to customizing PM is to let the craftsmen generate the PM program

from the ground up. What do they think? They are the ones who will be inspecting the

equipment, and if they think it should be looked at daily instead of weekly, this should be the

approach to take. It gives them ownership of the equipment and the empowerment to make it

work more reliably. When this comes together, look out. The results are significant gains in

equipment uptime. All equipment should be organized in this fashion according to what type of

material handling equipment it is. Even the racks should be a part of this (the air-operated flow-

through systems will need PM attention.) The air compressor will always be a part of a PM

program.

The final steps in the systematic approach to material handling maintenance are

validating results and return on investment. Companies should also identify priority areas for

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improvement based upon a total benchmark evaluation of the maintenance operation. They

should also take note of the common mistakes made by those charged with maintaining material

handling equipment and make sure that they are eliminated from the process. Of course, the

ultimate success will be determined by whether the customer is satisfied. Avoiding common

mistakes.

The most common and most obvious material handling maintenance mistake is to

operate in a reactive, firefighting mode.

The following are tips for avoiding other maintenance mistakes:

* Do not over lubricate and always be certain to use the correct lubricant.

* Do not assume that your craftsmen can automatically handle the new high-tech equipment.

They may need additional training and refresher courses from time to time. Develop an

individual training plan for each craftsperson based on his or her level of expertise.

* Use manufacturers' recommendations as a starting point for a PM program, but be sure that the

crafts-people themselves drive the program because they are most familiar with the demands on

the equipment and the inspection processes. In some cases, strictly adhering to manufacturers'

recommendations is counter-productive.

* How many spares should I have on hand? Make a concentrated effort to identify critical spares.

By critical, look at downtime cost and long lead times. If 100 people are scheduled to work on an

operation, then it must have spares to keep it in operations. Paint and plumbing supplies that are

10 minutes away are not critical spares.

* Keep manuals, documents, PM procedures and other inventories near the machines where they

can be used. This is valuable information and an effort should be made to organize it at the

machines. Successful organizations do this seriously, calling the process "facilitated assets."

With a systematic material handling maintenance approach that includes PM, a company

obtains a proactive planned maintenance operation. This operation can prevent common

maintenance mistakes and provide greater levels of service.

Best of all, it eliminates the firefighting mode that wastes scarce maintenance resources.

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Periodic Maintenance

Truck Frame & Chassis

Frame Damage

Counter Weight

Overhead Guard

Seat & Seatbelts

Tires

Data Plate

Upright Inspection

Channel & Rollers

Chains & Adjustment

Carriage

Forks

Load Backrest

Hydraulics

Operation

Oil Level

Hydraulic Cap

Filter Inspection

Hoses & Leaks

Linkages (if applicable)

Engine & Transmission

(I.C.E. Trucks Only)

Oil Level & Change

Lube Chassis, Chains

Filter

Air Filter (cleaned or replaced)

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Cap & Rotor

Points (if applicable)

Wires

Plugs & HR inspection

Leak inspection

Belts

Coolant

Radiator & Air Cleaner

Radiator Hoses

Governor & Carb. Linkage

Transmission Fluid Level

Differential

Linkage (if applicable)

Fluid & Filter Inspection

Brakes

Fluid Level

Pedal Height

Pedal Pad

Operation

Parking Brake

Electrical Systems

Gauges

Warning Lights

Battery Connection

Battery Condition

Wiring

Horn

Other Safety Features

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Hour Meter

Electric Trucks ONLY

Drive Motor Brushes

Hydraulic Motor Brushes

Power Steering Brushes

Contactor Tips & operation

Switches & Adjustments

Cables & Wiring Condition

Battery Connectors & Charger

SCR/Drive Control Panel Blowout

EQUIPMENT RECORDS

Equipment records play a critical role in effectiveness and efficiency of the maintenance

organization. Usually, equipment records are grouped under four classifications: maintenance

work performed, maintenance cost, inventory, and files. The maintenance work performed

category contains chronological documentation of al l repairs and preventive maintenance (PM)

performed during the item’s service life to date. The maintenance cost category contains

historical profiles and accumulations of labor and material costs by item. Usually, information on

inventory is provided by the stores or accounting department. The inventory category contains

information such as property number, size and type, procurement cost, date manufactured or

acquired, manufacturer, and location of the equipment/item. The files category includes

operating and service manuals, warranties, drawings, and so on. Equipment records are useful

when procuring new items/equipment to determine operating performance trends,

troubleshooting breakdowns, making replacement or modification decisions, investigating

incidents, identifying areas of concern, performing reliability and maintainability studies, and

conducting life cycle cost and design studies.

WORK ORDER SYSTEM

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A work order authorizes and directs an individual or a group to perform a given task. A

well-defined work order system should cover all the maintenance jobs requested and

accomplished, whether repetitive or one-time jobs. The work order system is useful for

management in controlling costs and evaluating job performance. Although the type and size of

the work order can vary from one maintenance organization to another, a work order should at

least contain information such as requested and planned completion dates, work description and

its reasons, planned start date, labor and material costs, item or items to be affected, work

category (preventive maintenance, repair, installation, etc.), and appropriate approval signatures.

JOB PLANNING

Job planning is an essential element of the effective maintenance management. A number

of tasks may have to be performed prior to commencement of a maintenance job; for example,

procurement of parts, tools, and materials, coordination and delivery of parts, tools, and

materials, identification of methods and sequencing, coordination with other departments, and

securing safety permits. Although the degree of planning required may vary with the craft

involved and methods used, past experience indicates that on average one planner is required for

every twenty craftpersons. Strictly speaking, formal planning should cover 100% of the

maintenance workload but emergency jobs and small, straightforward work assignments are

performed in a less formal environment. Thus, in most maintenance organizations 80 to 85%

planning coverage is attainable. Maintenance scheduling is as important as job planning.

Schedule effectiveness is based on the reliability of the planning function. For large jobs, in

particular those requiring multi-craft coordination, serious consideration must be given to using

methods such as Program Evaluation and Review Technique (PERT) and Critical Path Method

(CPM) to assure effective overall control.

USE OF COMPUTERS IN MAINTENANCE

Computerized maintenance management system (CMMS) is also known as enterprise

asset management and computerized maintenance management information system (CMMIS).

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A CMMS software package maintains a computer database of information about an

organization’s maintenance operations, i.e. CMMIS – computerized maintenance management

information system. This information is intended to help maintenance workers do their jobs more

effectively (for example, determining which machines require maintenance and which

storerooms contain the spare parts they need) and to help management make informed decisions

(for example, calculating the cost of machine breakdown repair versus preventive maintenance

for each machine, possibly leading to better allocation of resources). CMMS data may also be

used to verify regulatory compliance. CMMS packages may be used by any organization that

must perform maintenance on equipment, assets and property. Some CMMS products focus on

particular industry sectors (e.g. the maintenance of vehicle fleets or health care facilities). Other

products aim to be more general. CMMS packages can produce status reports and documents

giving details or summaries of maintenance activities. The more sophisticated the package, the

more analysis facilities are available. Many CMMS packages can be either web-based, meaning

they are hosted by the company selling the product on an outside server, or LAN based, meaning

that the company buying the software hosts the product on their own server.

Key features that a computerized system must have are -

• Hard copies of records must be available to be produced on request;

• The system must be tamper proof (e.g. records can't be changed at a later date);

• It needs to be clear what has been checked (which should be at least the items described

in the Guide to Maintaining Roadworthiness) and by whom;

• There is a clear end to end audit trail showing that identified faults are clearly logged

and once dealt with, signed off by a person who has authority to decide whether a vehicle is fit

for service.

Any planning tool software needs to be drawn up in accordance with the maintenance

regime agreed as part of the operator’s license requirements. If the computerized system does

not meet any of the above points then it will not meet the necessary requirements as identified by

the Guide to Maintaining Roadworthiness.

A first step Freight Best Practice offers a Guide to Preventative Maintenance and a free

simple planning spreadsheet to help you with improved maintenance. The Vehicle Maintenance

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Planner is an easy way to electronically track and store data on your fleet's maintenance helping

you to plan servicing, inspection and MOT schedules effectively and provide a log for any

unplanned maintenance your fleet may incur. This spreadsheet also provides a yearly planner

that can be printed and wall mounted.

1.The Daily Walkaround check

The daily walkaround check can be undertaken using a handheld device and

stored in an electronic format.

Providing a written report

Any defects found during the daily check, while the vehicle is in use or on its

return to base must be the subject of a written report.

The details that need to be recorded are:

• Vehicle registration or identification mark;

• Date;

• Details of the defects or symptoms; and

• The reporter's name.

It is common practice to use a composite form that also includes a list of the items

checked each day. It is advisable that where practicable the system should incorporate 'Nil'

reporting when each driver makes out a report - or confirms by another means that a daily check

has been carried out and no defects found. Electronic records of reported defects must be

available for 15 months along with any other record of repair. Hard copies must be able to be

produced where required.

Regular safety inspections:

Safety inspection information can be collected by the use of a handheld device

and stored electronically. The records MUST show a clear audit trail from inspection to repair

sign off – should one be required.

Safety Inspection Report Forms

Key Information

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A record must be completed for each safety inspection separately for both vehicles and

trailers. If the record of the safety inspection is to be stored electronically then the checklist used

for the inspection need not be retained. You may use an electronic device (e.g. PDA) in place of

a checklist.

Electronic Capture and Storage of Safety Inspection Data Electronic capture and / or

storage on computer of defects found or work done (e.g. bar coding or scanning), is acceptable

providing that a means of interpreting each code is readily available.

Safety inspection records stored electronically, using a computer, must be tamper-proof

and capable of producing hard-copy information for use at public enquiries held by Traffic

Commissioners. Computer records must contain:

• Name of owner / operator;

• Date of inspection;

Regular safety inspections

• Vehicle identity;

• Odometer (mileage recorder) reading (if appropriate);

• A full list of the items inspected (or these can be indicated on a paper report if used for

the inspection);

• An indication of the condition of each item inspected (however, it is sufficient to

provide details of defective items only)

• Details of any defects found;

• Name of inspector;

• Details of any remedial / rectification or repair work and by whom it was done; and

• A statement that any defects have been repaired satisfactorily. Internet-based systems

are becoming more common. These provide significant opportunities for improving the ease with

which operators can plan and monitor the maintenance of their vehicles, thus leading to higher

standards and improved compliance.

Safety Inspection Programme

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Safety inspections must be planned in advance. Vehicles that are subject to a

statutory annual test may have their year's programme planned around the anticipated test date to

avoid duplication of work associated with the test, such as cleaning and major servicing.

Planning a safety inspection programme :

A simple method of drawing up a programme is to use a year round planner or

flow chart. Computer-based systems are equally acceptable and electronic vehicle maintenance

record management and storage systems available will often incorporate an electronic planning

feature. The information, which should be kept in the simplest form possible and displayed

prominently, will serve as a reminder of programmed inspections or of any changes that have

been necessary. All vehicles subject to programmed attention should be included. Ideally

planners or charts should be used to set safety inspection dates at least six months in advance.

Vehicles' annual test dates should be included, as should servicing and other ancillary equipment

testing or calibration dates, e.g. tachograph, lifting equipment, etc. The planner should be

updated regularly by indicating the progress of the programme and recording any extra work

carried out. Vehicles that have been taken off the operator's licence or other vehicles temporarily

off-road should have their period of non-use identified, and a note should be made when vehicles

have been disposed of. The planner or chart may be used to record other items in the vehicle

maintenance programme, such as servicing, unscheduled work and refurbishing. Each activity

should be clearly identified.

Maintenance Engineer

The Maintenance Engineer enhances service quality and equipment reliability by

improving workflows and optimizing maintenance processes using Lean Six Sigma practices and

Reliability Centered Maintenance (RCM) methodology. This position, a key link between the

field maintenance organization and the engineering and manufacturing centers, provides input to

improve equipment design, reliability, and maintainability.

The Maintenance Engineer has a critical role in connecting field operations with the

maintenance organization, helping minimize downtime and failure rates and maximize

equipment productivity. This position reports directly to the Maintenance Supervisor or

Maintenance Manager.

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Essential Responsibilities and Duties

* Identifies and captures opportunities for improvement in equipment maintainability and

reliability.

* Uses Lean Six Sigma and RCM concepts to optimize work processes, adapt maintenance

tools and procedures to improve equipment utilization and reliability, and minimize

service quality incidents.

* Keeps current with latest equipment, technologies, and maintenance methods.

* Promotes importance of data and service quality within maintenance community.

* Assists with development and coaching of junior maintenance staff.

* Supports Maintenance Manager and Location Manager in planning for equipment and

maintenance resources and correcting existing discrepancies.

* Ensures application of asset management and maintenance systems data and accurate,

timely data entry and reporting.

* Participates in technical audits and compliance assessments, and follows up on closure of

remedial action plans.

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