CPM-PERT teknikleri ve uygulaması

Abstract

Bildiğimiz gibi bir projenin gerçekleşmesi, amacına ulaşması planlı, program, kontrollü ve titiz bir çalışmayla gerçekleşmektedir. Projenin amacına ve ölçeğine bakmadan, işletmelerin yerine getirmek zorunda olduğu görevleri vardırki bunlar kaba hatlarıyla planlama, organizasyon ve yönetme kalemleridir. Ancak bütün organizasyonların yapıldığı deneyimli ve gerekli eğitimden geçirilmiş ekibin kullanılmasıda her zaman projenin başarıya ulaşdığını veya normal yapım sürelerinde teslim edildiğini,sağlıklı ürünler elde edildiğini söyliyemiyebiliriz. Proje ye göre değişiklik gösteren hava, arazi koşulları, makine donanımı hasarları, beklenmedik pekçok olay projenin önünü tıkayan olumsuz etkileyen faktörlerdir.Bizim burda ele alacağımız kısım işletme sahibi gözüyle baktığımızda, proje sorumlusunun süre ve maliyet ilişkisi açısından etkin bir program ve denetim yapamamasıdır. Bu çalışmamızda genel proje yönetimi hakkında bilgi verdikten sonra tezimizin esas amacı birer yöneylem araştırması tekniği olan süre - maliyet optimizasyonu ve projelerin programlanmasında kullanılan CPM (Critical Path Method un baş harflerinden oluşan) ve PERT (Project Evaluation and Review Techniques in baş harflerinden oluşan) iki ayrı yöntemi ele almış bulunmaktayız. Bu iki yöntemden CPM deterministik, PERT ise probabilistik bir metodtur. Her iki yöntemde de faaliyet başlama zamanlarının ,proje tamamlanma zamanıyla olan ilişkileri incelenmektedir.Genelde bu yöntemlerinin uygulanması zaman alıcı ve tekrarlamalardan oluşan bir matematik sistemine dayandığı için hata yapmaya açıktır. Bu nedenle hızlı ve hatasız sonuçlar alınabilmesi için bilgisayar kullanımı daha uygundur.Çalışmamızda Microsoft bünyesinde bulunan MS project 2003 yazılımından yararlanılacaktır. Uygulama kısmında gelişim firmasının sözleşmeli müşterilerinden biri olan Mercedes Benz in 2007 yeni yıl hediyesi olarak müşterilerine vermeyi amaçladığı özel, daha önce piyasada olmayan değişik kapak, kağıt ve baskı sistemlerinin kullanılması zorunluluğu içeren 10.000 adet ajanda siparişi üretimi üzerine yapılmıştır. Sipariş veriliş tarihi 27 kasım 2006 olmakla beraber teslim tarihi 27 aralık 2006 olarak bir aylık bir süre belirlenmiştir.(normal işgünleri ve cumaertesi dahil ) Bütçe olarak 60.000 ytl nin üzerine %10 hizmet bedeli eklenerek müşteriye sunulmuştur. Gelişim firmasının elindeki diğer işlerin yetişmesi ve bu projenin maliyetininde en aza indirilmesi yeni yıl öncesinde kar marjını arttırmak amacıyla söz konusu projeye CPM-PERT yöntemi uygulanmış ve aynı projenin 20 işgününe tamamlanabileceği görülmüştür. Böylece firma elindeki diğer işlere kaynak aktarma sürecini hızlandırmıştır. Bu çalışmanın amacı modern proje programları ile etkin bir planlama ve denetim ile aynı kaynaklarla daha kısa sürede daha verimli çalışmalar elde edilebiliceğinin gösterilmesidir.

CPM AND PERT A project reaches its aim a defined time and sources if a planned, programmed and controlled working exist. A project can not be succeed if there are not experienced personel and enough equipment.This is normal time despite having experienced personel and enough equıtment..Bad meteorological and land conditions or other reasons effect to project negatively. But, also this main cause of delays is the fact that project menager can not make effective planning and control in terms of time and cost. İn this study, the necessity of an effective planing and control in surveying projects , as in all projects,is considered.Of all operation research technıques, CPM ( Critical path method ) and PERT ( Project Evaluation and Review Technıque ) methods are selected since they are more proper for the philosophy of surveying projects. İn application part of the study, here techniques are applied to a surveying project, performed before without using such project planing techniques, and the results are compared with ones, taken in the real project, with respect to cost and time. The main purpose of this study is to demostrate that the modern project programming methods, applied succesfully in printing house projects, can also be applied in the surveying projects and that, by means of effective planıng and control, a more productive work can be performed. 1- THE TERMiNOLOGY OF NETWORKS Critical Path Method (CPM), The critical path is a method of managing a project effectively. We have seen how the critical path is determined and how the float or slack is determined. Using the notion of float, the project manager can direct his or her efforts where they will do the most good activities that are found to have float, particularly those that have large amounts of float, can be managed less intensely than other activities in the project plan. This is because activities with float can be delayed without affecting the project completion date. Of course, activities that have large amounts of float can be delayed a considerable amount before they affect the project completion conversely, the activities that have zero float cannot be delayed without affecting the project completion date. These activities should be managed carefully by the project manager and the project team. İn the critical path method of managing projects, another term for float is ‘‘free float.’’ This is somewhat different than the float we have discussed up to now. The PERT system was developed for the Polaris Missile Program in the 1950s. At that time there was a lot of pressure on the United States Navy to complete the Polaris Missile Program. The Cold War was raging, and the United States needed a deterrent that would discourage the threat of nuclear war with Russia. A mobile missile that could be carried aboard a submarine and launched from beneath the surface of the sea would be a formidable weapon. The problem for the U. S. Navy was that there were two separate projects to be done. One was to develop a submarine that could launch these missiles. The second project was to develop a missile that could be launched from a submarine. The durations of the project plan activities had a great deal of uncertainty in them. The navy needed a method to predict the project schedule with better reliability than was possible in the past. PERT was developed to assist in analyzing projects where there was uncertainty in the duration of the tasks. İn This theses understanding PERT analysis, the PERT way to estimate, working with a network diagram (PERT chart) İn Step 1, we looked briefly at PERT analysis and showed you a diagram of how a project looks in a PERT chart. We also mentioned that in Microsoft Project 2003 a PERT chart is called a network diagram, and we looked at a project in network diagram view. İn this these we want to give you some background information about PERT,and then we will show you in detail how you can use project and PERT to do what if analysis. İn plain English, what if analysis, or PERT analysis, involves estimating how your project will go under the best of circumstances, under the expected circumstances and under the worst of circumstances. As we have mentioned, one reason for using project is to make a plan and then review it in order to avoid surprises. İf you do some what if analysis early in your project, you may be able to change your plan so that you are prepared for the worst of circumstances, or at the very least, you won’t be surprised when your worst nightmare comes true. Planing and Schedulıng wıth CPM require a reasonable accurate knowedge of time and cost for each ativity, fort he CPM network model is essentially deterministic. In many situations, the duration of an actıvıty cannot e accurately forecast, any time estimate being subjecttodubt . İf such an actvity lies on a noncritical path the usual CPM calculations remain valid, but there will be a local uncertainity in resource leveling and in the scheduling of men and materials, equipment and finance in those situations we have to use PERT, PERT introduces uncertainity into the time estimates for activity and project durations.it is therefore well suibed for those situations where there is either unsufficient backround information to specify accurately utility data or where project activities require research and development. Probability considerations are incorporated in project scheduling by assuming that the time estimate for each activity based on three different values: optimistic time, pessimistic time, most likely time. And these values help us to find an activity time called expected mean time. Pert uses expected mean time for each activity together with an associated measure of the uncertainity may be expressed either as the standart deviation or variance of the duration.The expected mean time is intended to be atime estimate having approximately a % 50 chance that the actual duration realized will be less, and % 50 chance that the actual duration will exceded it. From this point, it is clear that the formal determination of such activity data necessties using a probability distribution curve fort he activity completion times. Since n information actually exists regarding the probability distribution of the activity comletion times and since its determination is not feasible because of the activity durations are ubject random distrubances and delays, it is necessary to assume a probabılıty distribution curve. PERT can be used to good advantage in planning and control of any project involving uncertainty such as in research programs or unusual design and construction projects. And it can also be used to evaluate the alternative plans. İn many situations when a network model is being prepared for construction project it is not known before hand which of several alternative plans will be adopted for the completion of specific portions of the project. Each of these alternative plans will require specific and possibly different durations, resources, and so on and the arbitrary selection of one for inclusion in the network model may be misleading: It may be desirable therefore to build into the network model the uncertainty associated with the selection of the alternative plans, at is possible to introduce the uncertainty associated with alternative plans into the network model and the associated calculations for scheduled durations and resources, using probabilistic concepts. If, as is usual, we associate a probability of 1.0 for certainty on a scale ranging from zero to unity, then we can construe the zero probability as representing total rejection of an alternative or decision to implement a particular alternative plan. After project planning and project scheduling has been completed we have to think that the arrow diagram can be discarded as soon as the time schedule is developed. This is not so in fact, an important use of the arrow diagram occurs during the execution phase of the project .It seldom happens that the planning phase will develop a time schedule that can be followed exactly during the execution phase. Quite often some of the jobs are delayed or expedited, which naturally depends on actual work conditions. As soon as such disturbances occur in the original plan, it becomes necessary to develop a new time schedule for the remaining portion of the project. This section outlines a procedure for monitoring and controlling the project during the execution phase. İt is important to follow the progress of the projection the arrow diagram rather than solely on the time schedule. The time schedule is used principally to check if each activity is on time. The effect of a delay in a certain activity on the remaining portion of the project can best he traced on the arrow diagram.