Intended learning outcomes: Explain the transportation times matrix. Disclose a robust approximation of transportation time.
There are different techniques to determine transportation time between work centers (also called move time or transit time):
- Simple, but inexact: As a scheduling rule, planners use one single time that is not dependent on the work centers.
- Exact, but complex: A matrix of transportation times contains an entry for every combination: “preceding work center Û following work center.” This matrix should be maintained in the form of a table in a separate entity class. It is a square matrix containing zeros on the diagonal. If it is not dependent on the direction of the transport, the matrix will be symmetrical (see Figure 18.104.22.168). The difficulty with this technique lies in maintaining the two-dimensional table, since the number of work centers and the transportation times are continually changing.
Fig. 22.214.171.124 Transportation times matrix.
An efficient compromise between these two extremes is to use an approximation based on an analysis of transportation times, and that experience has been shown to be reliable, as in Figure 126.96.36.199.
Fig. 188.8.131.52 Approximation of transportation time.
- Within a plant, planners define a fictitious center and assume that each shipment must pass through this center. With this, the transportation time from one work center to another becomes the sum of the transportation time from the first work center to the fictitious center and the transportation time from the fictitious center to the other work center. As a result, you only have to register two attributes for every work center, and their values are not dependent on the other work centers.
This approximation is reliable, because the loading and unloading of the means of transportation comprise the greatest portion of transportation time. Actual transportation time from one work center to another varies little in relation to this.
- Between the fictitious centers of two plants, planners assume an additional transportation time. Again, for production facilities in the same region, this approximation is reliable, because loading and unloading of the means of transport make up most of the additional move time. In relation, the actual transportation time between the plants varies little.
- Characterizing plants by the attribute “region” will distinguish among plants in differing geographic areas. This allows differentiation among regional and interregional or even national and international shipments.
Course section 13.1: Subsections and their intended learning outcomes
Intended learning outcomes: Describe the order of the operations of a production order, operation time and operation load, the elements of interoperation time, administrative time, and transportation time.
13.1.1 Sequence of Operations and Network of Operations — The Order of the Operations of a Production Order
Intended learning outcomes: Describe a sequence of operations. Differentiate between a directed and an undirected network of operations. Identify a synchronization point.
Intended learning outcomes: Present the simplest formula for operation time using a graphic representation. Explain the simplest formula for operation load.
Intended learning outcomes: Identify the elements of interoperation time. Differentiate between technical wait time and nontechnical wait time. Describe transportation time.