With the complex of a huge number of jobs through an equally huge number of machines, the modern day job shop of sizable company needs the helps of Real time or Simulation system for efficient scheduling of the operation. The ultimate decision should be taken, by the section supervisor on the shop floor who is aware of things that a computer cannot be aware of, such as the human factors which can make things work when they do not seem to and vice versa, and many other subtle aspects and infrequent possibilities. The scheduling time horizon could be every shift or daily or weekly or some other time in between, all of which depend upon the shop’s characteristics such as order cycle time, average processing time etc.
The availability of computing machine has opened up avenues of quick digestion of a number of facts, their analysis presentation of possible decision alternatives, future scenarios under different assumptions etc all in a very short time so that our response to the situation is quick appropriate and timely. Time is the essence, and we have reached a stage where we can handle the dynamic situation in the actual plant with an equally response in order to take advantage from the situation or to at least reduce losses.
Scheduling in mass, continuous and project type production systems:
The scheduling aspects mentioned so far have been concerned with the job shop (open and closed shop) types of production in the main. It has been mentioned earlier that for a mass assembly line production (or continuous type), the planning problems, in both the time horizons – intermediate and short term – is one of setting the rate of production from the line and arranging the various production centers on the line accordingly. Line Balancing would be helpful in equalizing the output rates from the various work points on the mass production line and in reducing the idle time of labor. Unlike the job-order situation here the production control activity does not consist of following up each particular job order from one work center to another; rather it consists of maintaining an uninterrupted flow of the identical items as they go through the number of operations on the assembly/process line. It is like seeing that a stream of water flowing through a system of channels (converging into a major channel) does not get logged at any place. In a project type of production system, where one complex unit or item is to be produced involving a number of operations – many of them to be done one after the other in a sequence dictated by technology or limitations of resources, hence, the product developing its shape and getting value added as the time flows, the network analysis techniques such as PERT/CPM are quite useful in scheduling monitoring and control of production. While in a continuous or line production the flow is with respect to space, in the project type production the flow is with respect to time.
Line of Balance (LOB) Technique:
There is one variation of the project type production – a system where the project consists of producing a single batch of products where the delivery of the product is not at one point in time but is spread over many intervals of time according to a prior agreed schedule between the manufacturer and the customer. For example, a batch of boilers, a batch of combat aircraft, a batch of computers to be delivered according to a schedule, are the type of situations which all fall into this category. For the scheduling and control of it graphic technique called Line of Balance (LOB) is quite useful.
As is obvious from the above discussion, for LOB the following information is needed:
(1) The contracted schedule of delivery
(2) The key operations the making of the product, which need to be controlled
(3) The sequence in which the key events (of state or completion of operations) are connected.
(4) The expected/observed lead times of these events with respect to the completion of the final event, i.e. delivery of the finished product.