Conclusion and future work with solvent based Inkjet printing

113

MODULE 5 PUBLIC ANALYSIS TECHNIQUES

114

3.0 MAIN CONTENT

3.1 Origin and Meaning of CPM

The Critical Path Method (CPM) is a project modeling technique developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley, Jr. of Remington Rand. CPM is commonly used with all forms of projects, including construction, aerospace and defence, software development, research projects, product development, engineering, and plant maintenance, among others. Any project with interdependent activities can apply this method of mathematical analysis. Although, the original CPM program and approach is no longer used, the term is generally applied to any approach used to analyze a project network logic diagram.

On the other hand, PERT was developed for the US Navy Special Projects Office in 1957 to support the US Navy’s Polaris nuclear submarine project. It was able to incorporate uncertainty by making it possible to schedule a project while not knowing precisely the details and durations of all the activities. It is more of an event-oriented technique rather than start- and completion-oriented, and is used more in projects where time, rather cost, is the major factor. It is applied to very large-scale, one-time, complex, non-routine infrastructure and Research Development projects.

3.2 Basic Technique CPM

The technique is used in planning and control of well-defined projects or programme and their implementation, particularly with a simple management. It helps to determine the relationships between the activities and sequence of activities, in terms of what should be done first or later and the completion time. This scheduling activities is within a time frame and lead to event or milestone, and programme completion or achievement (terminus). Under CPM the earliest completion time of an event and the entire programme are determined. It helps to estimate time duration for the completion or various activities events and the entire programme.

The time duration of sequence of activities is the basis for the preference given for the programme or project by management when allocating resources. The basis for that preference is the activities and events critical to programme completion. Certain delays in those activities lengthen programme duration. The largest time duration and its completion determine that of the entire project, which the critical path is illustrated from the CPM diagram below:

115

In the CPM chart - above, the nodes represent major milestones and the arrows suggest the work needed to get to each milestone. More than one arrow pointing to a node indicates that all those tasks must be completed before the milestone has been met. A number is usually placed on the arrow “shaft” showing the number of days or weeks required for that task to be completed. Once you have drawn the CPM chart, it draws your attention to two points:

1. It allows you to see which tasks can be conducted simultaneously. For example, the process of collecting data often has “dead” periods, because you have to wait until mailed questionnaires are returned or because of the time lag between making an appointment for an interview and administering the interview. The CPM visualizes which other tasks you could conduct in such periods (for examples, refine your literature review).

2. It enables you to determine the pathway from start to end that takes the longest time to complete, which is called the “critical path” because any delay in an activity along that path will delay the end of the entire project.

However, there are software programmes now available in personal computers, designed for project management, which simplify

116

scheduling and charting the schedule.

3.2.1 Determining the Critical Path

From the diagram above, critical path is calculated, thus:

CRITICAL PATH = 1-3-4-7-8-9-End = 47 days (Longest duration) At Critical path, the slack period is zero.

SLACKS =0+2+3+4+7+8+E= 39, that is, 47-39=8days

=0+2+3+5+6+7+8+9+E=36, that is, 47-36=11 days

CRASHING THE CRITICAL PATH: Means shortening the durations of critical path activities by adding resources in order to perform more activities in parallel, resulting in decreased time spent for the project.

Crash duration is typically modeled as a linear relationship between cost and activity duration.

3.3 Basic Pert Technique

It is a planning and control technique based on network analysis. It is used for planning and organizing tasks and activities in relation to programme completion. PERT can be used to analyze the involved tasks in completing a given project, especially the time needed to complete each task, and to identify the minimum time needed to complete the total project. PERT was developed primarily to simplify the planning and scheduling of large and complex projects with multiple management. It is more concerned with activities or jobs.

PERT is similar to CPM in several ways. Both are flow charts. Both calculate expected completion times. Both determine the critical path. In fact, CPM can be subsumed in PERT analysis, because PERT involves CPM.

PERT, however, differs from CPM. First, it is concerned with events, unlike CPM that is concerned with activities. Second, PERT enables the calculation of variances in the expected completion times. In uncertainties, the most probable time for determining events can be determined. PERT is also more rigorous and sophisticated.

It is designed to manage large-scale and complex projects, with overlapping and multiple managements, logistic problems and imprecise objective. This is in contrast to CPM which is more applicable to a well defined programme with single management.

117