real time production monitoring system

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REAL TIME PRODUCTION M ONITORING SYSTEM

SIVA KUMAR S O SUBRAMANIAM

A thesis subm itted in fulfillment of the requirements for the award of the degree ofMaster of Science in Electronics Engineering

Faculty of Electronic Computer EngineeringUNIVERSITI TEKNIKAL MALAYSIA M ELAKA


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BSTR CT

production monitoring system is a system that is used in real time to recordproduction line problems. It is constructed using programmable logic controller andsensors to collect data from production lines. The real time production monitoringsystem is designed to collect data automatically and display the data on display boardsfor the workers to see. Devices in the real time production monitoring system arecapable of working as individual units or working together with multiple terminal linkssuch as automated machineries robotic systems and manual process line. The data willalso be relayed to the managem ent for prompt action.

Data on production time non-production time targets rejection rates plannedstops and cycle times will be displayed s well s relayed to the management.Unadulterated data co llected from the real time production monitoring system should berelayed to the management without human intervention. Such data would then beinterpreted accordingly in order to identify the faults at production level and to spurcorrective measures from the management. With the help of this real time productionmonitoring system the management will be able to monitor both the workers andmachine performance. Display of data can also prompt instant action from bothworkers and line supervisors.

The data collected is in line with the requirements of overall equipmenteffectiveness. Overall equipment effectiveness is the tool for improving efficiency.Efficiency of production lines enables better yield and utilization of the availableresources. The real time production monitoring system together with overall equipmenteffectiveness will help companies to generate higher revenue.


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BSTR K

Sistem pengawasan pengeluaran merupakan sistem yang digunakan di dalammasa nyata bagi merekodkan sebarang permasalahan yang berkaitan dengan talianpengeluaran. Ia dibina menggunakan sistem kawalan logik boleh aturcara PLC) danbeberapa pengesan bagi mendapatkan data daripada talian pengeluaran. Sistempengawasan pengeluaran masa nyata adalah direka untuk memperolehi data secaraautomatik dan memaparkan data pada paparan bagi membolehkan ianya dilihat olehpara pekerja. A lat peranti di dalam sistem ini adalah berkebolehan untuk berkerja samaada secara persendirian mahupun bekerjasama dengan beberapa rangkaian pangkalanseperti mesin berautomatik, sistem robot dan talian pengeluaran secara manual. Data-data juga akan dialirkan kepada pihak pengurusan bagi tindakan lanjut.

Data-data yang terlibat di dalam masa pengeluaran, masa bukan pengeluaran,sasaran pengeluaran, kadar tolak, pemberhentian berjadual, dan masa kitaran akandipaparkan dan dihantar kepada pihak pengurusan. Data-data asli yang dikumpulkanmelalui sistem pengeluaran masa nyata ini akan diagihkan kepada pihak pengurusantanpa campurtangan manusia. Data-data tersebut kemudiannya akan ditafsir bagimengenalpasti kelemahan di peringkat pengeluaran dan membolehkan pihakpengurusan mendapatkan pengukuran yang sepatutnya. Adalah difikirkan sesuaisekiranya data-data ini disambungkan terus ke dalam sistem komputer. Dengan adanyabantuan dari sistem pengawasan pengeluaran masa nyata ini, pihak pengurusan mampumengawasi kedua-dua pihak, samada pekerja mahupun kemampuan mesin. Melaluipaparan data ini, tindakan segera dari pekerja dan penyelia talian rnampu diperolehi.

Data-data yang terkumpul seharusnya setara dengan syarat-syarat keberkesanankeseluruhan peralatan. Keberkesanan keseluruhan peralatan merupakan alat ataumedium penarnbahbaikan kecekapan. Kecekapan satu-satu talian pengeluaranmembolehkan hasil yang baik diperolehi dan penggunaan sumber-sumber yang sediaada dipertingkatkan. Sistem pengawasan pengeluaran masa nyata digandingkan bersamadengan keberkesanan keseluruhan peralatan mampu membantu sesebuah syarikat dalammemacu keuntungan yang lebih tinggi.


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CHAPTER 1

INTRODUCTION

Production line inefficiencies are the main factors that contribute to less yield and henceless profit to any industry. The aim of this study is to design a real time productionmonitoring system for use on these production lines. Such a monitoring system will beused to automatically gather production line data and distributelsend it to the industrymanagement or anyone on the shop floor for instant action Kum ar et. al., 2007b). Theavailability of these da ta can help the industry in improving their production yield andhence profit.

1 1 The production line

A production line is a set of sequential operations established on a factory shopfloor whereby materials are put through a refining process to produce an end productthat is suitable for onward consumption or com ponents are assembled to make finishedgoods. In general a production process involves a moving platform or conveyor to movepartially completed products to workers who perform simple repetitive tasks designedto permit very high rates of production per worker.

Typically a production line system in industries can be classified into threewhich are robot and automated machines, semi automated machines humanmachines) and manual/work bench human).


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Production process using automated machineries or robots as shown in Figure1.1 are capital intensive as it uses a high proportion of m achinery in relation to workers.Capital is increased with fewer workers and faster rate of production. Machineries forautomated production process such as robots have high installation costs. Thus massproduction is ideally suited to serve large relatively homogeneous populations ofconsumers whose demand would satis@ the long production runs required by thismethod of manufacturing.

Figure 1 1 Automated production lines

Semi-automated production lines as shown in Figure 1.2 consist of human andmachineries working together to accomplish certain task. Such production lines arepracticed for moderate production output. The production process involves repetitivetask for both the humans and machineries to establish products within definitestandards.


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Figure 1 2: Semi automated production lines

Most of the work stations have their craftsman in the workbench Skilledworkers are required to follow procedures in producing parts Such production lines arepracticed for small scale production and manual assembly process A manualproduction line is shown in Figure 1 3

Figure 1 3: Manuallwork bench production lines


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1 2 Factors contributing to inefficiency of production lines

Analysis are carried out by the m anagement on production line problems almostdaily and counter measures a re brought to light to further strengthen the performance ofthis production line. Analysis is made easy when data is translated into variouscategories base on critical factors which affects the production lines. The factorsaffecting production lines can be categorized into three as shown in Figure 1.4. Each ofthese factors will results in various consequences towards the production lines.

Figure 1 4: Factors affecting production lines

1 2 1 Machine efficiency

Machine efficiency is one o f the factors that are overlooked by the managementand this can lead towards losses which reduces the yield Werner, 2004). Impropermaintenance of machines will result in low standards of production output and willincrease the maintenance of machineries Liker Jeffrey, 2004). Machines are meantto work efficiently but in some circumstances, machines can be less productive due toimproper preventive maintenance. Preventive maintenance is a key factor which keepsthe m achine running efficiently. The m aintenance activity on m achineries needs extraattention by the management to ensure the optimum usage of machineries and toeliminate unwanted w astages due to m achine stoppages.


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1 2 2 an power utilization

Human performance varies from time to time depending on their capability andduration of work. When the performance of a worker drops, the production output alsodrops. Improper monitoring of workers will result in low standards of production outputand will increase the maintenance of machineries. A major factor contributing to this isthe attitude of the workers themselves. Most of the workers tend to perform in anaverage manner and for most of the time they will be less productive and resultingtowards wastage of the production time. The only solution for this problem is to havebetter supervision on them during working hours.

1 2 3 Other factors affecting production line efficiency

The amount of time taken to solve faults on production line plays an importantrole in maxim izing the production output. On the race to meet the targets there will beunwanted breaks caused by m achines that will delay the production. In addition, time isalso wasted in the calling process and due to the department s unavailability to correctfaults.

In general, manpower capitalize most of the process on industries from themanagement to the laym an (operators). An industrial environment is one in which thereare a large number of people from various departments working together to meet setgoals. When it comes to unmet goals, fingers also should be pointed to the supportingdepartment which will be discussed in Chapter 3 The support department plays a rolein maintaining the consistent pace of work on the industrial shop floor.

There are three basic departments in industries which are the Total QualityManagement (TQM), Production Planning and Control (PPC) and maintenance. TheTQM involves all the quality matters of the parts produced. The PPC involves inplanning the production process and supplies based on orders. The maintenancedepartment is responsible on all the technical matters on the industrial shop floor. Mostof the industries face problem due to unforeseen damages that the com pany will face ifa task is not done on scheduled basis.


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1 3 Existing Production Monitoring System

Production monitoring is not new to the industry. Industries use it to improvetheir daily production output and at the same time to monitor their production lineoutcome.

The following methods are used in industries to provide information on thestatus of each w ork s tation, machineries or a production line. The devices and methodssuch as the Andon lights, etc will be discussed below. Each of the system has its ownbenefits and limitations.

1 3 1 Andon Lights

Generally Andon lights are used to provide visual indication on the productionline status. Green light indicates that the production is running smoothly. Yellow lightindicates various warnings such as material is required for on-going process orsupervisor attention is needed, etc. and red light indicates that the production is downnot in operation). These indicators can shorten the downtime by providing a faster

signal to supervision. Unfortunately, they do little to improve the productivity. The realtime production monitoring system incorporates this Andon lights as a downtimeindicator. The Andon light system is shown in Figure 1 5

Figure 1 5: Industrial Andon lights


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1 3 2 Goal and Variance Counters

A goal counter shows the set target for a length of time and a variance countershows the difference between the target and the actual output. An internal calculatormultiplies time by a preprograrnmed cycle time time taken to complete a certainprocess) to provide an instantaneous goal and variance. The disadvantage of a typicalgoal and variance counters is that they have no p rovision for entering a schedule whichallows tracking on the ac tual work times and breaks. When the device is switched ON,the goal counter increases based on elapsed time multiplied by programm ed rate. At theend of each shift, the system provides only working rate, rather than the performancetoward the necessary goals. These counters are not schedule based therefore workersgenerally have to control the start and stop of the system. The proposed counter systemis schedule based and runs automatically at the start of each shift. The productioncounters are shown in Figure 1 6

Figure 1 6: Production counters

1 3 3 ccept and Reject Counters

These counters provide operators or workers on the work station a real timevisual indicator of the actual production outputs. They can be part of an automaticmachine, whereby a seven segment display is used to indicate the numbers of acceptedand rejected parts. S ince these counters have no tim e base, it is difficult for the workersto determine whether they are on schedule. The accepted counter indicates to the


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workers how close they are to the set targets. The number of rejects indicates thatinstant action should be taken otherwise set targets will not be achievable. Both thesedata are very important to the management. The accepted and rejected counter is alsoincorporated into the real time production monitoring system. Figure 1 7 shown belowis an exam ple of some of the rejection and production status counters.

Figure 1 7: Rejection and production status counters

1 3 4 White Board or Tracking Sheets

A typically shop floor white board or tracking sheet is shown in Figure 1 8There are many varia tions of industrial shop floor tracking sheets or boards. Essentiallyall these sheets require operators line leaders and supervisors to mark down how manyparts were made in the past production hour. If a counter at the end of the productionline provides the information operators must reset this at the beginning of each sh ift toget the correct information. In most cases this system is operated without any countersattached to the production line. Som e operations count boxes o r use segmented trays toprovide this number. This system takes up valuable time because one operator shouldbe in charge of doing the counting and writing on the sheets at the sam e time.


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Figure 1 8: Production status ind ication board

1 3 5 Machine Controllers and Programmable Logic Contro ller PLC )

Automated work station or high end machineries often have a real timeproduction output tracking built right into the control system shown in Figure 1 9 Thisproduction output tracking s o h a r e is custom written for each machine and process sthat it can provide accurate real time information in a desired format. This comes at avery high initial cost. Generally, the production output tracking systems which uses aPLC or a computer based controlled machinery can track a limited number ofparameters on a fixed schedule. PLC s are great for collecting data, but not so good inanalyzing and presenting data. This must be done by a data acquisition system thatoften does not have the necessary information (such a s production schedule and cycletime) to provide mean ingful feedback.

Figure 1 9: PLC control software

9


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1 4 Real Tim e Production onitoring System

Real time production monitoring system should provide the right information tothe respective personnel at the right time. Presenting too much production informationto the production workers or operators is not essential to their task. With too muchunfocused inform ation thrown at them, workers or operators are not able to digest whatis necessary to modify on their current production outcomes. Whereby presenting toolittle information to the supervisors, supporting departments and the managers can belike watching the production operations through a keyhole. Each level of people in theindustrial shop floor have their role in keeping up to the set goals.

The m ost important requirements of any data collection and reporting system isthat the system is economical, accurate and easy to set up on a production line.Supervisors generally have an aversion to computer based systems because of ongoingheadaches with custom made software and other solutions. They are often morecomfortable with a production monitoring system PM S) which is capable of providingstraightforward connectivity to switches, sensors, PLC outputs and other commonindustrial equipments. If a PMS can be easily connected to each work stations andmachineries on a production line, then management needs for this critical data can beeasily satisfied. If the true production data can be au tomatically captured and presentedin a simple, understandable way to the operators, they will become a more integral partof the improvem ent process. An effective system should comprise of the followingthree elements:

Firstly a data collection device should be connected to automated, semiautomated or manual production line to count and collect data with minimal or nohuman intervention. Secondly there should be a display of the collected data. Thedisplay present relevant production information back to operators, line leaders,supervisors, the supporting departments and the management. Seven segment displaypanels have become popular with many industries because they can combine thebenefits of color with clear numerical values. Lastly the data collected should beanalyzed to provide sufficient production data for the management to conduct relevantanalysis at all level of the shop floor.


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The real time production m onitoring system consists of a real time display boardfor monitoring production line problems as shown in Figure 1 10 The productionmonitoring system is useful for displaying the production line targets, acts as a callingunit and be able to inform the m anagement on production line problems.

INPUTMACHINERIES

CONTOUTPUT

DISPLAY PAN ELOF REAL TIMEPRODUCTIONMONITORING SYSTEM

Figure 1.10: Block diagram of the real time production monitoring system

Data is co llected from process line machineries via a control unit normally madeup of PLC and are displayed on this display panel. The displayed data can also be sentvia compu ters to the industry administration.

A systematic and accurate online data collecting system for production lines isnecessary. The data gathered should be accurate in order to identify the various faultsat production level. Accura te monitoring of production lines enables better utilization ofthe available resources and hence efficiency. Data Collected may not be true due to theimproper monitoring, inaccuracy of the monitoring device and human intervention.Human intervention on the production data normally occurs when data is maneuveredto comply with the targets set by the management. Capturing and interpreting of thisproduction data without human intervention is a major challenge for the management.Hence an automatic data collecting system via PLC is necessary.

The data collected will be instantaneously displayed, using state-of- the artelectronics, so that attempts can be made immediately to rectify production lineproblems. The display can also be used to prompt workers to meet set targets. Contentsof display are as suggested by O verall Equipment Effectiveness OEE) requirements tobe discussed in chapter 2.


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1 5 bjective of study

The aim of this study is to design a real time system for monitoring productionlines. The system consists of a display unit capable of providing real time informationof production lines. The d isplay unit also displays targets to be met by operators on theproduction lines and acts as a calling device i.e. this will address the production lineproblems to their respective departments. Coupled to a systematic data collectionsystem for production lines, the production monitoring system will inform themanagement and the production teams on the faults as events happen.

A real time production monitoring system can save m anufacturers thousands ofRinggit RM) by increasing their production yield and optimizing the availableresources. The ability to monitor dozens of process line parameters, such s set goals,actual production output, cycle time, planned stop, rejection rate, non production timeetc can alert plant staff to changing conditions and can significantly decrease downtime.Continuous monitoring gives the workers and the supervisors a direct line of sight intoprocess line activity and enables them to keep up to the set goals. A good productionmonitoring system enables the respective personnel to solve production problemsquickly s event happens.

1 6 Scope of research

The research w as concentrated on the following areas.

1. Design and development of electronic circuitries to display production lineinformation s required by the industries based on OEE requirements.

2. Design circuits that are compatible with the control system of the productionline.

3 Develop a real time production monitoring system that is capable of capturing,displaying production line information and alert workers on production linefaults at all times.


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This study is conducted to further enhance the existing production monitoringsystem of production lines in a manufacturing company especially when there arehuman interventions on the production process. This study highlights the interruption ofproduction due to the departments involved in the production process. Example ofthese interruptions are machine break downs, problems due to quality, materials not instock and other major down turns due to poor manpower m anagement and machineryinvestments Werner, 2004 . Machinery investment is a vital consideration especiallyon the percentage of the returns compared to the invested value.

The primary literature in this study is the OEE. This study results in developing aproduction monitoring system that meets the requirements of OEE and comply witOEE calculations. Whatever data recorded from the production monitoring system isdirectly linked to OEE and the outputs are categorized into required measures andstandardize data for the managem ent


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CHAPTER

JIDOKA ND OVER LL EQUIPMENT EFFECTIVENESS

Numerous technologies are exploited in developing a reliable and eflicient real timeproduction monitoring system. The Andon systems in industries are far more advancedby integrating electronic devices with audio and color coded visual display. TheAndon system is one of the elements that make up the principle of Jidoka. Along with

that is OEE s a production tool that helps the industries in visualizing unforeseenlosses.

2 1 The concept of Jidoka

Jidoka is an ancient japanese term for autonomation which is automation with ahuman element. Jidoka refers to the principle of stopping work immediately when aproblem occurs. Jidoka involves the automatic detection of errors or defects duringproduction. When a defect is detected the halting of the production forces immediateattention to the problem. T he halting causes losing production but it is believed that thishelps to detect a problem earlier and avoids the spread of bad practices. Figure 2.1describes the concep t of Jidoka implemented on a production process (W erner, 2004).


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A machine detectsThe line is stopped a problem and

Daily improvementsManagerlsupervisor Improvementsremoves cause of the incorporated into thestandard workflow

Figure 2 1: Production life cycle on the concept of Jidoka

2 2 The concept of Andon

The Andon system is one of the elements that make up the principle of Jidoka.In the olden days Andon is a paper lantern which is a handy vertical collapsible paperlarnpshade with an open top and a candle placed at the central section of the closedbottom. To the ancient Japanese, Andon functions as a flashlight signaling devicefrom a distance or as a commercial sign Werner, 2004 .

Andon is a technical installation that supports the execution of a four stepprocess of abnormality handling as follows:

1 Detect the abnormality.2 Stop the process.3. Fix or correct the imm ediate condition.4. Investiga te the root cause and install a counter measure.


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Andon allows timely corrective actions by alerting personnel when abnormalconditions occur. Apart from that, the Andon system also allows shop floor teamleaders to spend less time and effort monitoring the situation and more time solvingabnormalities. Andon system does not only limit to that but also allows Operation teamsto monitor equipment and personnel more effectively. When Andon system isimplemented in the shop floor then this system can act as a two way communicationdevice for example when indicator returns to green this tells everybody that themachine or equipm ent is back to normal operation Pherson, 2006). Figure 2.2describes the Andon system Werner, 2004).

Andon boardSwitch operator)

Figure 2 2: The interaction of Andon system

Understanding the working principals of Andon system is simple and verystraight forward. If this system is implemented in the shop floor of the industries thenthe outcome is such:

1. Control the production.2. Operators have the ability to stop call wait calling device).3. Defect w ith report ability and correction where by the opera tors can report faults

immediately and countermeasures can be implemented at source.4. Workable design highlights problems with work density.


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The development of science and technology has seen many new technologiesbeing implemented. These results in the evolution of the production monitoring systemNowadays, the systems of Andon in many industries are advanced into electronicdevices with signboard incorporating signal lights, audio alarms, and text or otherdisplays installed at a workstation to notify management and other workers on faultsLiker Jeffrey, 2004).

2 3 Overall quipment ffectiveness

OEE has been considered the ultimate efficiency tool for equipments andmachineries used in industries. In 1971 the Japan Institute of Plant Maintenanceintroduced the Total Productive Maintenance TPM ) which includes the concept ofOEE as one of the important elements Giegling et. al., 1997). Nakajima thenintroduced the TPM to the United State of America in 1988 Sheu, 2006). OEE hassince gained a lot of attention as the ultimate performance measure of a piece ofequipment Gaboury et. al., 2001). Today OEE is one of the most important calculationtools for the managem ent in determining machine efficiency Pherson, 2006).Efficiency and effectiveness has different meanings. Because the originator of the OEEnamed it s overall equipment effectiveness, the industry keeps the same wordingalthough using it to refer to efficiency instead of effectiveness Sheu, 2006).

OEE can be used to save industries from making inappropriate machinepurchases, and help the management focus on improving the performance of theexisting machinery they already own. OEE is used to find the greatest areas ofimprovement which guide where to start with and shows the area that will provide thegreatest return on asset. The OEE formula will show how improvements inchangeovers, quality of products being produced, machine reliability improvements,working through breaks and more, will affect your bottom line Giese, 2007).

Understanding the concept and also elements which contributes towards OEEand how these elements will work together with the real time production monitoringsystem to improve the production yield is the core of study. A production monitoringsystem should meet the requirements of OEE and should comply with the OEE


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calculation. Whatever data recorded from the real time production monitoring system isdirectly linked to OEE and the outputs are categorized into required measures andstandardize data for the management.

OEE is a best practice metric for monitoring and improving the efficiency of themanufacturing processes such as machines, cells, assembly lines etc (Drickharner,2001). OEE is simple, practical yet powerful. It takes the most common sources ofmanufacturing productivity losses and places them into three understandable categorieswhich are Availability, Performance and Quality (Ziemerink Bodenstein, 1998). Bydoing so, it distills complex production data into simple understandable metrics thatprovide a gauge for measuring true manufacturing efficiency. It also forms thefoundation for tools that help to improve productivity. Figure 2 3 describes the basicmath s of OEE (Godfrey, 2002).

Availability rate X Performance rate X Quality rate

.Total hours planned Lost time Actual machine speed Num ber good productsTota l hours planned Design machine speed Total products made.

Figure 2 3: The basic math s of OEE

As the management strive towards the world class productivity in their facility,the simple OEE form ula will m ake an excellent benchmarking tool. The derived OEEpercentage is easy to understand and displaying this single number where all facilityand responsible personnel can view it, makes for a great motivational technique to alllevels. By giving the employees an easy way to see how they are doing in overall


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equipment utilization, production speed, and quality, they will strive for a higherproduction rate with the available resources (Koch, 1999).

Generally accepted world class goals or standards for each factor are differentfor each machine on industry. These individual factors will also vary every shift base onthe machines current overa ll performance. Studies have indicated that the average OEErate in industries is 60 . As shown in Table 2.1, a world class OEE is considered to be85 or better. Th is is a bench mark set by the Japan Institute of Plant Maintenance andwidely being practiced worldwide (Sheu, 2006). Clearly , there is room forimprovement in most manufacturing plants (Ramon, 2007).

Table 2 1: World class standards for each OEE factor (Ramon, 2007)

This research highly recommends using an automated production monitoringsystem with display for all the production related information. To the em ployee in eacharea, the PMS will become a common to glance at to visualize the actual productionperformance at all time.

OE E FactorAvailability ra tePerformance rateQuality rateOEE rate

2 4 alculation of Overall Equipment Effectiveness

World lass90.095.099.985.0

The basic parameters gathered from the manufacturing process which consistsof Availability, Performance, Quality and OEE are calculated for detail analysis (Bragg,2003). Most industries practice manually data collection and the hazel in this methodare in organizing this data into the required form. With the real time productionmonitoring system all the data required for OEE will be captured along the productionprocess and at the shift end, the responsible personnel need to key in the data into a


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standard formula used to ob tain the outcome of OEE Kum ar et. al., 2007). The basicbreakdown structure of production duration in industries is shown in Figure 2.4Ramon, 2007).

Figure 2 4: Breakdown structure of production dura tion

Plant Operating Time

OEE analysis starts with plant operating time which is the amount of time thefacility is open and ava ilable for equipment to operate Godfrey, 2002). The plantoperating time can be split into two categories which is planned operating time andplanned shut down as shown in Figure 2.5 Kumar et. al., 2007d). This includes allevents that should be excluded from efficiency analysis because there is no intention ofrunning production such s meal breaks, warm up time, scheduled maintenance orperiods where there is nothing to produce Costa et. al., 1997 . The remaining availabletime is the planned operating time Planned operating time is the proposed productiontime by the management Ram on, 2007).

Plant Operating Time

Planned Shut ownlanned O perating TimeOperating Time

Figure 2 5: Breakdown structure of production duration

Down TimeLoss

Planned O perating Time

SpeedLosset Operating Time

Planned Shut dow n

Fully ProductiveTime QualityLoss


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OEE begins wit planned operating time and scrutinizes efficiency andproductivity losses that occur, with the goal of reducing or eliminating these lossesHansen, 2001). There are three general categories of loss to consider which is down

time loss speed loss and quality loss Koch, 1999).

2 4 1 Availability

Availability takes into account down time loss which includes any events thatstop production process for an appreciable length of time, usually several minutes longenough to log s a traceable event Godfiey, 2002). This includes equipment failures,material shortages and changeover time. Change over time is included in OEE analysis,since it is a form of down time Pherson, 2006). While it may not be possible toeliminate changeover time, in most cases it can be reduced. The remaining availabletime is called operating time. So availability is the ratio of operating time which issimply planned operating time less down time to planned operating time and accountsfor down time loss s shown in Figure 2.6 Kum ar et. al., 2007d). Availability iscalculated s Costa et. al., 2002):

Figure 2 6: Breakdown structure of availability

Operating Time

Operating TimeAvailability Planned Production Time

Down TimeLoss

2 4 2 Performance

Performance takes into account speed loss which includes any factors that causethe process to operate at less then the maximum possible speed or rated speed when


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running Ramon, 2007). This includes machine wear, substandard materials, misfeedsand operator inefficiency Pherson, 2006). The remaining availab le time is called netoperating time. So performance is the ratio of net operating time to operating time andaccounts for speed loss as shown in Figure 2.7 Kum ar et. al., 2007d). Ideal cycle timeis the minimum cycle time that the process can be expected to achieve under optimalconditions for a given part Godfrey, 2002). Therefore when it is multiplied by totalpieces the result is net operating time. Ideal cycle time is som etimes called design cycletime or nameplate capacity. Since rate is the reciprocal of cycle time, Performance iscalculated s Costa et. al., 2002):

Net O perating Time SpeedLoss

Figure 2 7: Breakdown structure of performance

Ideal Cycle Time Total Pieces)Performance = Operating Time

Total Pieces Operating Time)Performance Ideal Cycle Time

2 4 3 Quality

Quality takes into account quality loss which accounts for produced pieces thatdo not meet quality standards including pieces that require rework Kum ar et. al.,2 0 0 7 ~ ) .The remaining time is called fully productive time Godfrey, 2002). Theultimate goal is to maxim ize fullyproductive time Pherson, 2006). Quality is the ratioof fully productive time which is the time for good pieces produced to net operating


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tim time for total pieces) as shown in Figure 2.8 Kumar et. al., 2007d). Quality iscalculated as Costa et. al., 2002):

Figure 2 8: Breakdown structure of quality

Fully ProductiveTime

Good PiecesQuality Total Pieces

QualityLoss

2 4 4 Overall Equipmen t Effectiveness

Availability, performance and quality combine into one OEE score and thissingle number provides a complete measure of machine efficiency Gaboury et. al.,2001). OEE is the ratio of fully productive time to planned production time Pherson,2006). OEE is calculated s Sheu, 2006):

OEE Availability Performance Quality 2.5)

OEE can also be calculated by reducing the earlier formula to the simplest termsPherson, 2006):

Good Pieces Ideal Cycle Time)OEE Planned Production Time


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This is an alternative way of calculating OEE and with a bit of reflection and bymultiplying goodpieces by ide l cycle time will results in a nett productive time that isrequired to produce only good pieces without down time Pherson, 2006). Bothequations 2.5) and 2.6) will give the same figure of OEE s the end result Pherson,2006). When it comes to detailed analysis, the best equation to use is equation 2.5)which will be used to analyze the details of OEE s in equation 2.1) 2.4). Equation2.6) is an indicator of the OEE value of a certain machine.

AVAILABILITY

OVERALLEQUIPMENTEFFECTIVENESSQUALITY

PERFORMANCE

Figure 2 9: The elements of OEE

2 5 Losses due to ignorance of Overall Equipment Effectiveness

The major goals of OEE are to reduce and/or eliminate the six big losses, themost comm on causes of efficiency loss in production Gaboury et. al, 2001). Table 2.2lists the six big losses and show how they relate to OEE loss categories. Addressing thesix big losses and som e of the events that contribute towards these losses is an essentialtask for the management, whereby the responsible personnel can focus on ways tomonitor and correct them Konopka Trybula, 1996). Categorizing data makes loss

real time production monitoring system

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